head to head · open source
sim vs vellum-assistant
sim has 29,680 GitHub stars, 3,843 forks, 336 open issues and last shipped today. vellum-assistant has 1,292 stars, 187 forks, 179 open issues and last shipped yesterday. sim leads on adoption by 2,197% (29,680 vs 1,292 stars). sim is written in TypeScript under Apache-2.0; vellum-assistant is written in TypeScript under MIT. sim has attracted 13% as many forks as stars, vellum-assistant 14%. sim was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 1 topic tag (anthropic), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| sim | vellum-assistant | |
|---|---|---|
| GitHub stars | ★ 30K | ★ 1.3K |
| License | Apache-2.0 | MIT |
| Written in | TypeScript | TypeScript |
| Last push | 2026-09-20 | 2026-09-19 |
| Forks | ⑂ 3.8K | ⑂ 187 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick sim if
- You weight community size — 30K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches TypeScript
- You value the larger contributor base for long-term maintenance
pick vellum-assistant if
- You want the vellum-assistant feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches TypeScript
- You evaluated both and vellum-assistant fits your workflow better
About sim
Sim is an open source collaborative workspace for building, deploying, and monitoring AI agents and workflows. It lives in the TypeScript ecosystem and is distributed under the Apache 2.0 license, with a repository that has accumulated roughly 29,600 stars and 3,800 forks over its two year history. The project positions itself as a single surface where chat, workflows, tables, files, and knowledge coexist, whether accessed through a browser or a desktop application for macOS.
About vellum-assistant
Vellum Assistant is an MIT licensed, TypeScript personal AI assistant for individuals and small teams who want a persistent, self improving agent that runs across desktop, mobile, web, voice, email, Telegram, Slack and Twilio without building the memory and orchestration layer themselves.
read the full vellum-assistant overview →
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Frequently asked questions
Is sim or vellum-assistant more popular?
sim has 29,680 GitHub stars and vellum-assistant has 1,292. sim has the larger community by that measure.
Are sim and vellum-assistant free?
Both are open source. sim is licensed under Apache-2.0 and vellum-assistant under MIT. Neither carries a licence fee.
What is the difference between sim and vellum-assistant?
sim is written in TypeScript and vellum-assistant in TypeScript. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, sim or vellum-assistant?
Choose sim if you want the larger community (29,680 stars) or its Apache-2.0 licence terms. Choose vellum-assistant if its feature set, stack or MIT licence fits better. Both are self-hostable.