Open source

Open-source note-taking: what the licence actually buys you

An open-source note-taking app is one whose source code is published under a licence that lets you read, modify, run and redistribute it. That matters for notes specifically, because a note archive is a decades-long asset: if the software is open, it can be forked and kept alive regardless of what happens to the people who wrote it.

Open format is not the same as open source

This distinction gets blurred constantly, and it is the single most useful thing to be clear about. An open format means your data is readable without the vendor's software — markdown files in a folder, for instance. An open source means the software itself is published and can be run by anyone.

Obsidian has the first and not the second: your vault is plain markdown on your disk, which is a genuinely strong data-ownership position, but the application is proprietary and its source is not published. If the project stops, you keep your files and lose your editor. Logseq, Joplin, Trilium, AppFlowy, AFFiNE, SilverBullet and Nodum have both.

Which one you need depends on what you are protecting against. Open format protects your data. Open source protects your workflow.

MIT, AGPL, and source-available — the practical difference

Most open-source note apps sit in one of three buckets, and the differences are not academic.

Permissive (MIT, Apache-2.0) — do almost anything, including building a closed product on top. Nodum and AFFiNE are MIT; SilverBullet is MIT.
Copyleft (AGPL-3.0) — you may run and modify it, but if you offer it as a network service you must publish your changes. Logseq, Joplin, Trilium and AppFlowy are AGPL. This is a deliberate choice to keep hosted forks open, and it is a real constraint if you intend to build commercially.
Source-available — the code is readable but the licence restricts use, so it is not open source in the OSI sense even though it looks like it at a glance. Anytype has spent most of its life here.

The open-source options, honestly placed

There is no single winner, because these tools disagree about what a note is.

Logseq (AGPL) — local-first outliner, block references, flashcards. Best if you think in bullets.
Joplin (AGPL) — notebooks, tags, end-to-end encrypted sync to storage you own, the best Evernote importer there is. Best if you are leaving Evernote.
Trilium / TriliumNext (AGPL) — self-hosted, deep hierarchy, note cloning, a real scripting API. Best if you want to program your notes.
AppFlowy (AGPL) and AFFiNE (MIT) — the Notion-shaped ones: pages, databases, and in AFFiNE's case an infinite canvas.
SilverBullet (MIT) — the minimal self-hosted web PKM: one process over a folder of markdown, extended with Lua.
Nodum (MIT) — browser-native, multi-tenant, Obsidian-compatible markdown with wikilinks, automatic backlinks, a GPU knowledge graph, collaboration, publishing and an MCP server.

What makes Nodum's position different

Nodum is MIT licensed end to end — the FastAPI backend and the Next.js frontend both — with no open-core split, no paid tier holding features back, and no contributor licence agreement assigning rights elsewhere. The repository is the product.

It is also the open-source option that is web-native rather than a desktop app with a sync service bolted on. That is what makes it usable on a locked-down work laptop, a Chromebook, and a phone, all against the same vault. Self-hosting is one Docker Compose command that brings up the API, Postgres, Redis, MinIO and a Caddy edge with automatic TLS.

And the exit is real: export gives you a folder-true zip of .md files — the same thing an Obsidian vault is — so choosing it does not commit you to it.

How to check an app is actually open source

Find the LICENSE file in the repository — not the marketing page.
Check whether the licence is OSI-approved, or merely 'source available'.
Check whether the whole product is open, or only a client while the server is proprietary.
Look for an open-core split: are the features you need behind a paid, closed tier?
Check the export path works before you need it.
Check whether there is a self-hosting guide that someone has actually followed.

Questions people ask

What is the best open-source note-taking app?

For local-first outlining, Logseq. For leaving Evernote, Joplin. For a self-hosted hierarchy with scripting, Trilium. For a Notion-shaped workspace, AppFlowy or AFFiNE. For browser-based linked notes with backlinks and a knowledge graph, Nodum — MIT licensed, self-hostable, and storing Obsidian-compatible markdown.

Is Obsidian open source?

No. Obsidian is proprietary software. Its vault format is open — plain markdown files in a folder — but the application source is not published. Nodum is MIT licensed across both frontend and backend, which is why it can be forked, audited and self-hosted.

Is there an open-source alternative to Obsidian?

Yes, several. Logseq is the closest local-first one. Nodum is the closest web-based one: it uses the same [[wikilink]] syntax, imports and exports Obsidian vaults as zips, and adds a GPU-rendered knowledge graph, collaboration and publishing — all under the MIT licence.

Does open source mean free?

Usually in practice, but not by definition — open source is about rights, not price. Nodum is both: free to use and MIT licensed. If you self-host it, your only cost is the server it runs on.

Comparing specific tools

All 18 are on the alternatives index. Terms used on this page are defined in the glossary.

Start tying things together.

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