Open source knowledge base software

Two of the best-known "open source" knowledge base tools are not what a reader assumes. Outline is licensed under the Business Source License, not an open source licence at all, and Docmost gates features behind a paid plan even when you run it on your own server. Neither fact is hidden, but neither is obvious from a repository badge.

Licences, feature gates and prices below were checked directly against each project's own LICENSE file, source tree and pricing page on 22 August 2026, not read from a badge or a summary.

Knowledge base software sits next to the same self-hosting decision this site works through for a feedback board in self-hosting a feature request board.

What does "open source" actually mean for each of these?

Sorted by licence and what is free, because that is the question a badge does not answer.

Is Outline actually open source?

No, and its own licence says so. Outline is licensed under the Business Source License 1.1, and the restriction is explicit: you may not use the Licensed Work "for a Document Service", a commercial offering that lets third parties create their own teams and documents. That is a real, enforceable limit on what you can build with the code, the opposite of what "open source" normally means. The licence converts to Apache-2.0 on 13 July 2030, but until then, anyone calling Outline open source without qualifying it is simply wrong. Plenty do.

The Business Source License (this document, or the "License") is not an Open Source license.

Business Source License 1.1, in Outline's own LICENSE file

Outline also sells a hosted version directly: Starter at $10 a month for one to ten people, Team at $79 a month, Business at $249 a month. A BSL-licensed project also selling its own cloud is not unusual, it is closer to the point of the licence, which exists to stop a third party reselling the same code as a competing hosted service before 2030.

Does Docmost really charge for self-hosted features?

Yes, and this is the sharper version of the open-core pattern. Docmost is AGPL-3.0, and the free Community edition genuinely includes pages, databases, kanban boards, realtime collaboration, search and public sharing when self-hosted. What it holds back is SSO, page-level permissions, AI and MCP support, the Confluence importer, attachment indexing and MFA, all behind the paid Business plan at $3.50 a seat a month billed yearly, with a 10-seat minimum, a $35-a-month floor. That applies whether Docmost runs on its own cloud or a server you provisioned yourself. AGPL guarantees you can read, run and modify the code; it says nothing about which features the maintainer gates behind a subscription, even on your own infrastructure.

What is MkDocs Material's Insiders programme?

A sponsorship-gated tier layered on top of a genuinely free tool. MkDocs Material is MIT, 27,311 stars at the time of checking, and builds to static files using Python at build time, so the free version needs no server at all. Insiders sits behind GitHub Sponsors and includes four plugins not in the public release: optimize, privacy, git-revision-date-localized and git-committers. The sponsorship tiers, and whether any Insiders feature later merges into the free release, could not be confirmed, that part of the page is client-side rendered. The base MIT tool is unaffected either way: everything needed to build and host documentation ships free.

Which of these are genuinely unencumbered?

Three, cleanly. Docusaurus, MIT, 66,041 stars at the time of checking, builds to static files with Node only needed at build time, and carries no paid tier or gated feature at all. MkDocs Material's free build, separate from Insiders, is the same shape: MIT, static output, Python only at build time. Both parallel how a static support centre works, nothing running once the files are built, covered from the other direction in static site or server.

BookStack is the third: MIT, 19,003 stars at the time of checking, and unlike the two static generators it needs a running server, PHP 8.2 or later with MySQL 8 or MariaDB 10.6, for people editing pages together rather than committing Markdown files. Nothing in its feature set is held back for payment. Worth knowing before filing an issue: BookStack's development has moved to Codeberg, and the GitHub repository now carries a banner saying so, with GitHub left as a mirror.

Wiki.js sits alongside them on licence terms, AGPL-3.0, 28,788 stars at the time of checking, no paid tier or gated feature found. It needs Node and a database, the same shape as Docmost without the seat-priced paywall.

What do the hosted alternatives cost?

For teams who would rather pay someone to run any of this.

Zendesk's figures are quoted in GBP, not USD, because the pricing page geo-redirected to a UK price during this check; say which currency you saw. Zendesk Guide is also not sold on its own: it comes packaged inside the wider Zendesk Suite, so the GBP 45 a month figure buys the whole helpdesk platform, not a standalone knowledge base. Nuclino's and HelpKit's paid pricing could not be verified and are left out rather than guessed.

Which one should you actually use?

It depends on one question: does anyone need to edit in a browser? If not, a static generator is the entire answer and everything else here is machinery you do not need. Docusaurus and MkDocs Material's free build both need nothing running once built, both unrestricted MIT, and the choice between them is really ecosystem, React and MDX against Python and Markdown, not licence or cost.

If people need to edit together in a browser, with permissions and realtime collaboration, you are running a server whichever tool you pick, and the licence question above decides the shortlist. BookStack and Wiki.js give you that without a seat-priced paywall. Docmost's free Community edition is genuinely capable, provided you can live without SSO, page permissions, AI features and MFA, or absorb the $35-a-month, 10-seat-minimum floor. Outline is the one to read the licence on first: fine to self-host internally, explicitly off-limits for reselling as your own hosted document service before 13 July 2030.

Docket is not a knowledge base tool and is not part of this comparison; it is a support centre for bugs, feature requests and a changelog. But the split above, static against a server needing permissions and realtime state, is the same line this site draws for its own category in static site or server.

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