Restack Open Call (2027-01R)

Restack Open Call 2027-01R is a Horizon Europe supported cascade funding programme administered by NLnet to support R&D that strengthens an open, resilient and trustworthy internet technology stack. The call offers initial project grants normally between €5,000 and €50,000 (with larger follow-up grants possible) from a total Restack programme budget of €7 million and funds projects of 1–12 months duration. Applications must be submitted via the NLnet proposal system before 3 January 2027 at 12:00 Brussels time and funded outputs must be published under recognised free or open source licences. Proposals must demonstrate a strong European dimension, typically by allocating at least 60 percent of project funds to contributors resident in Horizon Europe eligible countries.

What it funds

Small to medium R&D projects that produce production-ready open-source building blocks for an Open Internet Stack (hardware, software, tooling, packaging, security, standards work and related activities). Outcomes must be released under recognised free or open licences.

Who can apply

Open to individuals and organisations of any type worldwide provided the proposal demonstrates a clear European dimension (teams from Horizon Europe-eligible countries should receive at least 60% of the funds). No legal entity required to apply.

Key dates & how to apply

Apply via the NLnet proposal form. Read the Guide for Applicants and NLnet's Generative AI policy before submission; use of GenAI in proposal writing is disallowed except for accessibility reasons.

Assessment and support

Two-stage evaluation with external review and an independent review committee. Projects scored on technical excellence, relevance/impact and value for money. Selected projects receive mentoring and optional support services (security audits, accessibility, licensing, packaging, community support).

Footnotes

1. 1Full eligibility, maximums and conditions are in the Restack Guide for Applicants and eligibility pages available at nlnet.nl

Basic facts

Who can apply and eligible applicant types

Eligible applicant types (detailed)

Funding mechanism and amounts

Consortium requirement and project structure

Geographic and beneficiary scope

Target sectors and topics

Eligible activities and technical scope (examples)

Project maturity / expected project stage

Application process and submission

Evaluation, selection criteria and stages

For a proposal to move from stage 1 to stage 2 the total weighted score must be above 5.0 out of 7. Projects that remain competitive after stage 2 are subject to final validation by the independent review committee.

Number of application stages and timeline

Success rates

Success rates are not provided as explicit percentages. The programme is competitive and limited by available budget. Projects that fail the knock-out eligibility are immediately excluded. Because the Restack programme runs multiple small rounds and funds many projects, applicants should expect moderate to low success probability per submission; strong alignment to strategic potential, excellent technical merit and clear European dimension improve chances.

Co-funding and eligible costs

Nature of support and additional services

Licensing, openness and AI policy

All project outcomes must be made available under recognised free/open licences and scientific outputs as open access. Software and hardware must be released under open licences and follow open standards. NLnet has a strict Generative AI policy: the use of generative AI is not allowed during writing of proposals (with an accessibility exception), and GenAI-generated artefacts are not allowed as project deliverables. Read-only use of GenAI tools for code checks is permitted with transparency requirements; costs for AI use are ineligible.

Conflict of interest and exclusions

NLnet staff and organisations within the Restack consortium are excluded from applying. The review process is performed by independent, full-time professional reviewers and validated by an unpaid independent review committee comprised of external domain experts. Members of the review committee and their relatives are excluded from submitting proposals. There are explicit institutional conflict of interest rules documented in the Guide for Applicants.

Application tips and practical guidance

Important constraints and limits

Where and how to apply

Summary — what is this opportunity about and why apply?

Restack is a cascade funding programme within the Open Internet Stack initiative, funded by Horizon Europe and administered by NLnet Foundation. It provides small-to-medium R&D grants to accelerate the development, maturation and scaling of production-ready open-source and open-hardware building blocks that together constitute a trustworthy, interoperable, deployable and maintainable internet stack. Restack supports projects across the technology stack that contribute demonstrably to digital autonomy, operational resilience and permissionless innovation. Grants range from €5,000 to €50,000 for first proposals with pathways to larger funding for proven outcomes. The programme combines monetary support with expert non-financial services, operates an open and frequent round schedule, and requires clear open-licensing, accessibility and a demonstrable European dimension.

Footnotes

1. 1Full guidance, the list of Horizon Europe-eligible countries and the Restack Guide for Applicants are available on the Restack landing page: nlnet.nl and NLnet's fund portal nlnet.nl. These pages include the definitive list of eligible countries and detailed application instructions.

Executive summary

Restack is a Horizon Europe supported cascade funding opportunity for research and development that strengthens an open, resilient and trustworthy internet technology stack. It supports operational digital commons across the full technology stack, including open hardware, core internet infrastructure, middleware, software services, local first infrastructure, security, supply chain integrity, standards and end user applications. The call is particularly suitable for practical open source projects that reduce vendor lock in, improve user autonomy and create reusable building blocks for Connected Collaborative Computing networks.1

The call offers project grants normally requested between €5,000 and €50,000 for an initial proposal. Projects with proven potential may subsequently seek larger support, subject to the programme conditions. The total Restack programme budget is €7 million, and the programme is intended to operate through successive calls until the available budget is allocated.2

The deadline for this call is 3 January 2027 at 12:00 Brussels time. Applications are submitted through the NLnet proposal system rather than directly through the standard EU Funding and Tenders Portal.3

Opportunity profile

What the funding is intended to support

Restack addresses the structural dependence of digital society on proprietary, closed or difficult to replace technology components. Its objective is to help establish an open internet stack that is deployable, scalable, secure, interoperable and capable of supporting digital autonomy and permissionless innovation.4

The opportunity is deliberately broad across technology layers, but proposals must make a concrete contribution to the Open Internet Stack and must have research and development as their primary objective. Projects should normally produce practical, reusable and publicly available results rather than only commercial services or closed internal improvements.

Illustrative areas of interest

Eligible activities

Eligible activities can include the following, provided that they are cost effective, technically credible and directly linked to Restack objectives:[ [FN:5] ]

Design and development of free and open source software or open hardware.

Validation, testing or constructive investigation of existing or novel technical solutions.

Software engineering that adapts technology to new use cases or improves quality, maintainability and reliability.

Formal security proofs, security audits, testing frameworks and continuous integration.

Technical documentation, educational materials and documentation for users, developers or researchers.

Standardisation activities, including relevant membership fees for standards bodies.

User requirements analysis, usability work and inclusive design.

Packaging and other measures needed to support wider deployment and adoption.

Participation in relevant technical and developer events, including eligible admission, travel and subsistence costs.

Project management and other activities supporting robust software development and deployment practices.

Essential infrastructure costs incurred directly for the project.

Activities that are primarily marketing, proprietary product development, routine commercial operations or development of a closed component are not aligned with the stated purpose of the call.

Who can apply

The call is unusually open regarding applicant status. Individuals, informal collectives, associations, not for profit organisations, academic or research groups, public sector bodies, SMEs and other organisations may apply. A separate legal entity is not required, and the opportunity is not restricted to universities or established research institutions.6

The applicant must demonstrate the ability to carry out the work, provide a credible budget and work plan, and accept the requirement that funded results be made openly available. Applicants should also be able to enter into the grant memorandum of understanding with NLnet and satisfy any requirements concerning identity, contracting, payment and legal capacity.

European dimension

A strong European dimension is an eligibility condition for Restack. The stated practical test is that people contributing to the project who are resident in Horizon Europe eligible countries should receive at least 60 percent of the project funds. The benefit of the project to Europe by itself is not sufficient if the funded project team does not demonstrate this dimension.7

The eligible country concept is broader than EU Member States and includes Horizon Europe associated countries and certain other eligible countries and territories. Applicants should verify the current Horizon Europe eligibility position before submission, particularly where the team includes contributors outside the European Union.

Exceptional proposals from outside the relevant geographic area may be considered where the proposer has unique technical expertise and the proposal is of exceptional quality, but this should be treated as an exception rather than the normal route to eligibility.

Funding amounts and financial conditions

The normal first grant request is between €5,000 and €50,000. The call description specifically seeks proposals in this range, making it appropriate for focused technical work, feasibility and validation activities, targeted improvements to an existing open source project, or a clearly bounded development milestone.

A first proposal may request up to €50,000. A proposal above €50,000 must normally be preceded by one or more successfully completed smaller projects funded through Restack or an equivalent programme such as an NGI programme. The earlier work must have publicly released its deliverables under recognised open or free licences, addressed relevant accessibility expectations, and satisfactorily dealt with the outcomes of any required independent security audit.8

The maximum grant per proposal is €150,000. The maximum aggregate amount that may be granted to one third party over the lifetime of Restack is €500,000. These are ceilings rather than entitlements, and the amount offered may be lower than the amount requested.9

There is no stated fixed EU reimbursement rate or automatic percentage of eligible costs. The support is calculated as the amount necessary to achieve the key objectives, taking account of projected cost, expected value, cost effectiveness, ineligible expenditure and any additional activities requested during assessment. The final amount is recorded in the memorandum of understanding between NLnet and the grantee.

The available material does not specify a universal co financing requirement, standard overhead rate, mandatory institutional contribution or fixed payment schedule. Applicants should therefore present a complete and economical budget and should not assume that indirect costs or general overhead will automatically be accepted.

The grant is described as a donation administered by a recognised public benefit organisation. The tax treatment may depend on the recipient and its jurisdiction, so applicants should obtain local tax advice before relying on any particular treatment.10

Projects above €50,000 may be subject to a full independent security audit at the end of the project. Payment of part of the grant may be made conditional on the audit outcome and on satisfactory remediation of identified issues.

Assessment and selection

The process has two substantive assessment stages followed by independent review. Initial eligibility checks operate as knockout criteria. Proposals failing alignment, research and development requirements, the European dimension or another mandatory condition are not scored further.

Initial scoring

The first substantive assessment uses the following weighted criteria:

The weighted score must be above 5.0 out of 7 to proceed to the second stage. Passing this threshold does not guarantee funding, because proposals are subsequently ranked against the quality of the round and the remaining budget.

Second stage

The second stage focuses on strategic contribution and lasting impact on the Open Internet Stack. Reviewers may ask clarification questions, request evidence, suggest minor improvements, compare the proposal with related projects, examine proposed rates and milestones, and assess the sustainability and adoption pathway of the results.

The review team may independently verify technical claims, methods, facts, relationships with upstream projects and the existence of complementary efforts. The proposed budget and milestones may change during this process. If the applicant cannot respond within the allocated period, the proposal may be moved to a later call.

Independent review

Projects selected for funding are checked by an independent review committee comprising experts from the internet and open source fields, academia and the public sector. The committee verifies eligibility, budget frugality and other concerns. A project may be returned to a later call if the committee identifies unresolved issues.

Open source, open science and intellectual property requirements

All scientific outcomes must be published as open access. Software and hardware developed with support must be released in its entirety under a recognised free or open source licence. Proposals that intend to open source only a minor component while retaining the main project as proprietary are not aligned with the programme.11

Applicants should select licences that are legally workable, compatible with project dependencies and suitable for long term reuse. They should also explain how source code, hardware designs, documentation, build instructions, data and other outputs will be published and maintained after the funded period.

The programme values open standards, interoperability, reproducibility and sustainable maintenance. A strong proposal should identify relevant upstream projects, standards bodies and user communities and explain how it will contribute back rather than create an isolated fork or incompatible implementation.

Generative artificial intelligence conditions

The NLnet Generative AI policy states that generative AI may not be used to write the proposal or to provide answers during interactive evaluation. This includes generating ideas and restructuring, shortening or translating proposal text. An accessibility exception exists for applicants who rely on AI based assistive technology, but such use must be disclosed.12

Generative AI may not be used to produce funded artefacts such as code, designs or documentation. Read only use, such as checking code for possible security issues, may be allowed if the applicant performs the actual fixes and remains transparent about the use. Applicants must disclose known past and present generative AI use at project level and disclose whether an existing codebase contains or is expected to contain a significant amount of AI generated code.

Costs incurred for generative AI use are not eligible. Funded contributors remain responsible for correctness, security, clarity and reproducibility. The policy permits other forms of automation, including deterministic code generation, formal and symbolic proofs, fuzz testing and non generative machine learning, where these are otherwise relevant to the project.

Application process and expected information

Applications are submitted through the NLnet proposal form. The form requests a concise project overview, requested amount, budget breakdown, tasks and effort estimates, rates, comparison with existing and historical efforts, technical challenges, ecosystem and user information, applicant experience, other funding sources, optional attachments and generative AI disclosures.13

The proposal should be written in English and in the applicant's own words. The application form indicates that the project summary is limited to 1,000 characters, while several explanatory sections have limits of up to 2,000 or 4,000 characters. Attachments are optional, should not replace a self contained proposal and may be submitted in formats such as HTML, PDF, ODF, images or plain text within the stated total size limit.

The proposal should be short, concrete and technically specific. It should clearly identify the problem, the open source or open hardware result, the users, the technical work, measurable deliverables, dependencies, risks, budget logic, European dimension and route to adoption.

Recommended proposal structure

Define the infrastructure or digital commons problem and explain why it matters for an open internet stack.

Describe the proposed technical solution and distinguish it from existing projects, standards and historical approaches.

Set out a work plan with tasks, effort, milestones, deliverables and acceptance criteria.

Explain who will use the results, how contributors and upstream projects will be engaged, and how adoption will be supported.

Provide a lean budget tied to specific tasks and explain the rates and any external costs.

Explain the licensing, publication, governance, maintenance, security and accessibility approach.

Show how the team satisfies the European dimension, preferably by identifying contributors and the proportion of funds allocated to eligible countries.

Risks and points requiring careful attention

The strongest formal risk is failure of the European dimension. A project with an excellent technical idea may still be ineligible if at least 60 percent of funds are not normally allocated to contributors from Horizon Europe eligible countries.

A second risk is proposing a scope that is too broad for the requested amount or duration. Restack favours value for money, practical results and a clear contribution. A small number of demonstrable deliverables is likely to be more credible than an ambitious but weakly bounded platform rebuild.

A third risk concerns openness. The applicant should be able to release the complete relevant result under a recognised open source or open hardware licence. Proprietary dependencies, restrictive data, undisclosed patents or a plan to open source only selected modules should be addressed before submission.

A fourth risk concerns security, accessibility and reproducibility. Projects should budget or plan for testing, documentation, packaging, accessibility and security work where relevant. Larger projects may face an independent security audit and conditional payments.

A fifth risk concerns generative AI compliance. Applicants should prepare the proposal without generative AI unless the accessibility exception applies, disclose relevant codebase history and ensure that funded artefacts are produced by human contributors rather than generated by AI.

A sixth risk is budget uncertainty. The requested amount is not automatically awarded, and the final grant may be adjusted during evaluation. Applicants should avoid inflated rates, unexplained overheads and costs that are not necessary to achieve the stated objectives.

Strategic assessment

Restack is a strong fit for an applicant that can deliver a clearly defined open technical result within 1 to 12 months and demonstrate direct relevance to foundational internet infrastructure, interoperability, security, privacy, reproducibility, deployment, standards or user autonomy.

The opportunity is less suitable for a project whose main purpose is commercial product development, closed service delivery, generic artificial intelligence development, marketing, non technical community activity or research without an open and reusable result.

The strongest applications are likely to combine technical excellence with an explicit ecosystem strategy. Reviewers are expected to examine whether the work complements rather than duplicates existing efforts, whether upstream maintainers and users support the approach, whether the result can be adopted in practice and whether the requested budget is proportionate to the expected impact.

Practical applicant checklist

Confirm that the work is primarily research and development and directly contributes to the Open Internet Stack.

Confirm that the project result can be released fully under a recognised free or open source licence.

Identify the contributors and demonstrate the European dimension, normally with at least 60 percent of funds allocated to contributors in Horizon Europe eligible countries.

Keep the first request within €5,000 to €50,000 unless the applicant has already completed qualifying smaller work through Restack or an equivalent programme.

Prepare a task based budget with realistic rates and no unsupported overhead assumptions.

Define concrete milestones, outputs, users, testing arrangements and publication locations.

Compare the proposal with existing projects and explain what is new, better integrated or strategically important.

Identify security, accessibility, licensing, privacy, dependency and maintenance risks.

Review and comply with the NLnet Generative AI policy before writing and submitting the proposal.

Submit through the NLnet proposal system before 3 January 2027 at 12:00 Brussels time.

Official sources

The authoritative EU Funding and Tenders Portal record identifies the opportunity, deadline, duration, total budget, project acronym, grant agreement and cascade funding status.

The full Restack call page, applicant guide, eligibility page, European dimension guidance and generative AI policy should be read together because the portal record provides only a high level summary of the requirements.

Restack main call page: NLnet Restack

Restack applicant guide: Restack Guide for Applicants

Restack eligibility information: Restack Eligibility

Application form: NLnet Submit a Proposal

European dimension guidance: European Dimension

Generative AI policy: NLnet Generative AI Policy

Footnotes

1. 1Official Restack information describes the objective as delivering, maturing and scaling operational internet commons across the technology stack, including open hardware, middleware, local first infrastructure and end user applications. Source: NLnet Restack.
2. 2The Restack applicant guide states that the programme will competitively award €7 million in grants and operate from 1 June 2026 to 30 May 2030, with calls continuing until the budget is allocated. Source: Restack Guide for Applicants.
3. 3The official call information identifies 3 January 2027 at 12:00 Brussels time as the single stage deadline, while the NLnet application page identifies the NLnet proposal system as the submission route. Sources: EU Funding and Tenders Portal Restack Open Call and NLnet Submit a Proposal.
4. 4The Restack main page describes the Open Internet Stack as a foundation for resilient, trustworthy and strategically autonomous digital infrastructure and connects the fund to the European Commission supported Open Internet Stack initiative. Source: NLnet Restack.
5. 5The eligible activity list is set out in the Restack eligibility information. Source: Restack Eligibility.
6. 6The NLnet and NGI descriptions state that the call is open to individuals, SMEs, academics, public sector bodies, non profits, communities and other organisations. Source: NGI Open Calls.
7. 7The European dimension guidance defines the practical benchmark as people from Horizon Europe eligible countries receiving at least 60 percent of the funds. Source: European Dimension.
8. 8The Restack applicant guide sets the conditions for proposals above €50,000, including successful completion of earlier smaller projects, open publication, accessibility compliance and satisfactory treatment of security audit findings. Source: Restack Guide for Applicants.
9. 9The Restack applicant guide states a maximum of €150,000 per proposal and €500,000 per third party over the lifetime of the programme. Source: Restack Guide for Applicants.
10. 10The applicant guide describes grants as donations made by NLnet as a recognised public benefit organisation. Tax treatment remains dependent on the recipient and applicable national rules. Source: Restack Guide for Applicants.
11. 11The applicant guide requires scientific outcomes to be open access and software and hardware to be released in their entirety under recognised open source licences. Source: Restack Guide for Applicants.
12. 12The restrictions on proposal writing, funded artefacts, transparency and read only use are set out in version 2.0 of the NLnet Generative AI policy dated 20 October 2026. Source: NLnet Generative AI Policy.
13. 13The NLnet application form requests the project summary, budget, task breakdown, rates, comparison with other efforts, technical challenges, ecosystem, team experience, other funding, attachments and AI disclosures. Source: NLnet Submit a Proposal.