head to head · open source
sim vs vellum-assistant
sim has 29,984 GitHub stars, 3,883 forks, 336 open issues and last shipped yesterday. vellum-assistant has 1,477 stars, 232 forks, 179 open issues and last shipped yesterday. sim leads on adoption by 1,930% (29,984 vs 1,477 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 16%. 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 | ★ 1.5K |
| License | Apache-2.0 | MIT |
| Written in | TypeScript | TypeScript |
| Last push | 2026-11-04 | 2026-11-04 |
| Forks | ⑂ 3.9K | ⑂ 232 |
| 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
A workspace to build, deploy and manage AI agents and workflows. Quickstart Cloud hosted: sim.ai Self hosted Open Desktop: macOS macOS 12+, Apple Silicon and Intel. See the desktop docs to point it at a self hosted deployment. Capabilities Connect 1,000+ integrations and every major LLM Add Slack, Notion, HubSpot, Salesforce, databases, and more Build agents visually, conversationally, or with code Ingest files, knowledge bases, and structured table data Monitor runs, logs, schedules, and workflow activity One workspace, every surface Chat and workflows are just the start — tables, files, and knowledge all live…
About vellum-assistant
A personal AI assistant that evolves with you. 8 different types of memory (episodic, semantic, procedural, emotional, prospective, behavioral, narrative, shared) make it truly yours. It learns how you work, remembers what matters, and takes action across your apps. What It Does If you've set up a Personal AI on OpenClaw, Hermes Agent, or Claude Code, you know how long it takes, and how many times you have to hatch a new one to get it right. Vellum gets you the result you're looking for out of the box, one download away. Get Started 1. Sign up or download the app The desktop app is available for macOS and…
read the full vellum-assistant overview →
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Frequently asked questions
Is sim or vellum-assistant more popular?
sim has 29,984 GitHub stars and vellum-assistant has 1,477. 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 (29,984 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.