A block-based personal knowledge management system, honestly reviewed. Built for people who want Notion’s feel without Notion’s servers.

TL;DR

What it is: Open-source (AGPL-3.0) personal knowledge management system with block-level editing, bidirectional links, and end-to-end encrypted sync — written in TypeScript and Go [1][3].
Who it’s for: Privacy-conscious knowledge workers, researchers, and founders who want Notion’s UI and feature set without their data sitting on someone else’s servers [3][4].
Cost savings: Notion Plus runs $10/month per user. SiYuan’s core is free, self-hosted, and runs on a $6/month VPS or your existing NAS [3].
Key strength: Closest thing to a Notion clone that you can run entirely offline or on your own hardware. One reviewer switched from Notion to SiYuan running on a Synology NAS and reported zero learning curve [3].
Key weakness: AGPL-3.0 license (not MIT) is a legal blocker for embedding in commercial products. Cloud sync is a paid add-on from the SiYuan team. Plugin ecosystem is smaller than Obsidian’s. No real-time multi-user collaboration.

What is SiYuan

SiYuan is a privacy-first personal knowledge management (PKM) system. The core model is blocks: everything you write — paragraphs, headings, lists, code snippets, tables — is a discrete content block with a unique ID. Those blocks can be referenced, linked, and embedded anywhere in your knowledge base, giving you the bidirectional linking that tools like Roam Research popularized, but inside a WYSIWYG editor that looks and feels like Notion [1][3].

The project is developed by the B3log team (a Chinese open-source software organization), written in TypeScript for the frontend and Go for the backend, and published under AGPL-3.0 [1]. As of this review it has 41,931 GitHub stars and 2,675 forks, putting it in the same tier as Logseq on GitHub [1].

Unlike Obsidian — which is proprietary software with a free license for personal use — SiYuan’s source code is fully open. Unlike Logseq — which is also open source but graph-first and text-file-based — SiYuan stores data in a custom SQLite-backed format and renders a Notion-style document interface [4]. That’s the key design bet: SiYuan trades Obsidian’s “plain Markdown files you can open in any editor” portability for a richer, more Notion-like experience with block IDs and cross-document references that plain text files can’t support.

The result is a tool that one XDA reviewer described as feeling like “another instance of Notion with minor tweaks” — which is either its greatest selling point or a reason to avoid it, depending on what you want [3].

Why People Choose It

The reviews converge on a single reason: people want Notion’s experience without Notion’s cloud dependency.

The Notion privacy problem. Notion is not open source. Every note you write syncs to Notion’s servers, and you’re trusting Notion not to lose your data, not to raise prices, and not to read it. For people working with sensitive research, client data, or personal journals, that’s a real concern — not a paranoid one [3][4]. The Privacy Guides community thread [4] notes that SiYuan meets the criteria that matter: client-side open source, E2EE for sync, and standard export formats.

It actually looks like Notion. This sounds shallow but it matters for adoption. The XDA reviewer who switched to SiYuan running on a Synology NAS specifically called out that it uses “the same color scheme, the same left-indented sidebar with nested folders, the same tabbed UI at the top to access multiple notes at once” and that it “did not have to spend more than a few minutes to familiarize” themselves with the interface [3]. Most Notion alternatives either look worse (Joplin) or require a mental model shift (Logseq’s graph-first approach, Obsidian’s file-and-folder structure). SiYuan doesn’t.

It runs on a NAS. This is the deployment use case that shows up repeatedly. SiYuan ships as a Docker image, and Docker runs on Synology, QNAP, Unraid, and TrueNAS out of the box. If you already have a NAS at home, you can run SiYuan on it without spinning up a separate VPS [3]. For self-hosters who’ve already invested in local infrastructure, this is a no-brainer.

Offline-first. SiYuan stores all data locally and works fully offline. The cloud sync is optional and end-to-end encrypted when used — but you don’t need it. This is the opposite of Notion’s architecture, where offline support is limited and secondary [1][4].

Features

Most core features are free, including for commercial use, per the README.

Block editing:

Every element — paragraph, heading, list item, code block, quote, table, math formula — is a first-class block with its own ID [1][3]
Block-level references and bidirectional links with a backlinks panel [1][3]
Blocks support custom attributes [1]
20+ block types, 10+ inline element types [website data]
Focus mode: zoom into any block, navigate context via breadcrumbs [website data]
Dynamic loading for documents up to millions of characters [website data]

Organization and navigation:

List outline mode for hierarchical note-taking [1][website data]
Collapsible headings and outline blocks [website data]
Graph view for visualizing connections between documents [3]
Full-text search across all blocks [1]

Memory and review:

Built-in spaced repetition using the FSRS algorithm — the same algorithm used by Anki [1][website data]
Flashcard creation directly from blocks [website data]

Database:

Database blocks with relations, rollups, and templates — roughly analogous to Notion’s database feature [1][website data]
Two databases can link to each other via relation fields [website data]

AI integration:

OpenAI API integration for writing continuation, translation, summarization, grammar correction, and Q&A [1][website data]
The reviewer at XDA confirmed this works with ChatGPT [3]

Sync and privacy:

End-to-end encrypted cloud sync (paid add-on from SiYuan team) [1][4]
WebDAV and S3-compatible storage support for self-managed sync [1]
Mobile app that can act as a local server — so your phone and computer can sync over LAN without going through the internet [website data]

Extensibility:

Plugin and theme marketplace built into the app [3]
Widgets (iframe-based) for extending block functionality [3]

Pricing: SaaS vs Self-Hosted Math

SiYuan core software: Free, AGPL-3.0. The application itself, all core features, AI integration hooks, databases, spaced repetition — all free [1].

SiYuan cloud sync: The official cloud sync service is a paid add-on. Exact current tier pricing is not available in the sources reviewed — check https://b3log.org/siyuan/pricing.html for current rates. The important point is that the cloud sync is optional: you can sync via your own S3 bucket, WebDAV server, or NAS without paying anything [1][website data].

Self-hosted infrastructure cost:

NAS you already own: $0 incremental
A fresh VPS for SiYuan only: $5–10/month (Hetzner, Contabo)
A domain + reverse proxy: ~$10/year for the domain, nginx/Caddy is free

Notion for comparison (2026 pricing):

Free: limited features, 7-day history
Plus: $10/month per user (billed annually)
Business: $15/month per user
Enterprise: custom pricing

Concrete math for a solo founder:

If you’re paying $10/month for Notion Plus and you switch to self-hosted SiYuan on a $6 Hetzner VPS, you save $48/year after VPS costs — which isn’t the headline number. The real savings come for small teams: two people on Notion Plus costs $240/year. Self-hosted SiYuan on the same $6 VPS costs $72/year (VPS + domain), regardless of how many users you add. At five people, Notion costs $600/year; SiYuan still costs $72.

The caveat: SiYuan is primarily a personal PKM tool, not a team wiki. If you’re looking for real-time collaborative editing (multiple cursors, live edits), SiYuan doesn’t offer that. That’s a different category.

Deployment Reality Check

Docker is the standard path, and it works [3]. The README documents Docker, Unraid, and TrueNAS hosting. The XDA reviewer ran it on a Synology NAS without drama [3].

What you need:

A machine running Docker (NAS, VPS, home server, Mac)
About 512MB RAM for a personal instance (the container is lightweight)
A reverse proxy (Caddy or nginx) if you want HTTPS access from outside your LAN
An access token/passcode (SiYuan has built-in auth via access code)

What can go sideways:

The AGPL-3.0 license matters more than people realize. AGPL requires that if you deploy SiYuan as a network service and modify the source code, you must publish those modifications. For personal use, this is irrelevant. For a company building a product on top of SiYuan or embedding it in a commercial offering, it’s a hard stop — you either keep your modifications open or you negotiate a commercial license [4].

SiYuan stores data in its own SQLite-backed format, not plain Markdown files. This is the core architectural trade-off. Your notes are not raw .md files you can open in VS Code or migrate to Obsidian with a drag-and-drop. SiYuan supports export to Markdown, PDF, Word, and HTML, but your working format is proprietary-ish. The Privacy Guides community confirmed it exports to standard formats [4], but the internal format is SiYuan’s own.

The sync story has a wrinkle the website doesn’t advertise loudly: if you’re self-hosting, you’re managing your own sync. The E2EE cloud sync from the SiYuan team is the easiest path, but it’s paid. Rolling your own with WebDAV or S3 works but requires setup and has occasional conflict-resolution edge cases that the community forums discuss [4].

Plugin quality varies. The marketplace has a growing catalog, but it’s nowhere near Obsidian’s plugin ecosystem, which has been building for years. If you depend on specific Obsidian plugins (canvas, advanced tables, dataview), those equivalents may be partial or missing in SiYuan.

Realistic setup time: 30–60 minutes for a technical user on a machine that already runs Docker. For someone setting up Docker for the first time, budget a full afternoon.

Pros and Cons

Pros

Genuinely looks and feels like Notion. The learning curve for Notion users is near zero — same sidebar structure, same block model, same tabbed document interface [3]. This is rare in the alternatives space.
Fully offline capable. Works without internet, without any server, without any account. Your data doesn’t leave your machine unless you configure sync [1][4].
E2EE sync when you use it. Whether you use the official sync service or configure your own S3/WebDAV endpoint, sync is end-to-end encrypted by design [1][4].
Runs on commodity NAS hardware. Synology, QNAP, Unraid, TrueNAS all supported out of the box [3][website data]. If you already have home server infrastructure, SiYuan adds zero marginal cost.
Spaced repetition built in. The FSRS-based flashcard system means you don’t need a separate Anki workflow — you can create review cards directly from your notes [1][website data].
Database feature is real. Not just tables — relational databases with cross-database links and rollup fields, comparable to Notion databases [1][website data].
41,931 GitHub stars and active commit history (last commit within hours as of this review) [1]. Not an abandoned project.
Free for commercial use (the software, not necessarily the cloud sync) [README per merged profile].

Cons

AGPL-3.0, not MIT. You cannot embed SiYuan in a commercial product without either open-sourcing your modifications or getting a commercial license. This rules it out for founders building products on top of it [4].
Proprietary internal data format. Notes are not plain Markdown files. Export exists, but your daily working format is SiYuan-specific. Migrating away later means export + cleanup [4].
No real-time collaboration. Multiple users can access the same SiYuan instance, but there’s no Google Docs-style concurrent editing. This is a PKM tool, not a team wiki [1].
Cloud sync is paid. The easiest sync path (SiYuan’s official service) costs money. Free sync requires self-managing WebDAV or S3, which adds complexity [1][website data].
Smaller plugin ecosystem than Obsidian. Obsidian has been building its community plugin catalog since 2020. SiYuan’s marketplace exists but has less depth, especially for power users with niche workflows.
Chinese-origin documentation. The official website is Chinese-first. The English community forum (liuyun.io) and GitHub Issues are active, but if you need documentation for edge cases, you’ll sometimes encounter machine-translated content [1][3].
Block ID format creates friction for plain-text workflows. If you write something in SiYuan and export it, the exported Markdown will have SiYuan-specific block ID attributes. Not a dealbreaker, but worth knowing.

Who Should Use This / Who Shouldn’t

Use SiYuan if:

You’re a Notion user who wants an offline-first, self-hosted replacement and doesn’t want to relearn a new paradigm.
Privacy is a genuine constraint — regulated industry, sensitive research, client data you can’t put on third-party servers.
You have a NAS or home server already running and want to add a knowledge management system without paying for a VPS.
You want spaced repetition integrated into your notes without maintaining a separate Anki setup.
You’re a solo user or a very small team (2–3 people) who can share a self-hosted instance.

Skip it (use Obsidian) if:

You need your notes as portable plain Markdown files that work in any editor.
You live in a plugin-heavy workflow and need access to a mature extension ecosystem.
You prefer open formats over a richer feature set.

Skip it (use Logseq) if:

Your thinking is inherently graph-shaped and you want to build a knowledge graph, not a document hierarchy.
You want Org-mode or plain text as your working format.
You’re coming from a Roam Research workflow.

Skip it (use AppFlowy or Affine) if:

You need real-time collaborative editing for a team.
You want a Notion alternative with a more permissive open-source license (AppFlowy uses AGPL too, but Affine is MIT for parts of the project) [2].

Stay on Notion if:

Your compliance team won’t approve self-hosted infrastructure.
You rely on Notion’s public pages, guest sharing, or API integrations with your existing stack.
You have more than 5–10 people who all need concurrent editing with granular permissions.

Alternatives Worth Considering

Obsidian — local-first, large plugin ecosystem, plain Markdown files, but proprietary software (not open source). Better for power users who want format portability.
Logseq — open source, graph-based, plain text files. Better for outliner-first thinking, worse for document-style writing.
AppFlowy — open source (AGPL-3.0) Notion alternative with multi-user support. More collaborative than SiYuan but heavier to self-host [2].
Affine — open source, combines notes and whiteboard, real-time collaboration, local-first [2]. Closer to a Notion + Miro hybrid.
Joplin — mature open-source note-taking with E2EE sync and Markdown. Simpler and lighter than SiYuan, but no block model or bidirectional links.
Notesnook — end-to-end encrypted notes, cross-platform, open source. Simpler scope than SiYuan, better for straightforward note-taking [1].
Notion — the incumbent. Best collaboration, largest integration catalog, no self-hosting, $10+/user/month.

For a privacy-focused solo founder or researcher, the real shortlist is SiYuan vs Obsidian vs Logseq. Pick SiYuan if you want the Notion experience and don’t need plain-text portability. Pick Obsidian if portability and plugin ecosystem matter more than privacy licensing. Pick Logseq if graph-based thinking is how your brain works.

Bottom Line

SiYuan is the most faithful open-source reproduction of the Notion experience available today. If “I want Notion but on my own server” is the actual sentence in your head, SiYuan is the closest match — not just in features, but in how it feels to use it day-to-day [3]. The block model, the sidebar, the database support, the graph view: it’s all there. And it runs on a NAS you already own.

The trade-offs are real. AGPL-3.0 means no embedding in commercial products without legal review. The internal data format means you’re committing to SiYuan’s ecosystem. Sync requires either paying for their cloud service or self-managing your infrastructure. And if you’re expecting Notion’s collaborative features or Obsidian’s plugin depth, you’ll be disappointed.

But for the specific user — privacy-conscious, already comfortable with Docker, looking for an offline-first PKM that doesn’t require relearning how to take notes — SiYuan delivers exactly what it advertises. The 41,931 GitHub stars aren’t from people who stumbled into it by accident.

If deploying it is the blocker, that’s precisely what upready.dev handles for clients — one-time setup, you own the server.

Sources

OpenAlternative — SiYuan: Open Source Alternative to Notion, Obsidian and OneNote. https://openalternative.co/siyuan
OpenAlternative — 10+ Best Open Source Nuclino Alternatives in 2026. https://openalternative.co/alternatives/nuclino
Sumukh Rao, XDA Developers — “I replaced Notion with this open-source alternative that even runs on my NAS” (May 17, 2025). https://www.xda-developers.com/this-open-source-notion-alternative-runs-entirely-on-your-nas/
Privacy Guides Community Forum — “SiYuan - Privacy-first Notebook” (April 2024 thread). https://discuss.privacyguides.net/t/siyuan-privacy-first-notebook/17855

Primary sources: