head to head · open source
cobalt vs Zulip
cobalt has 43,316 GitHub stars, 3,798 forks, 269 open issues and last shipped 6 months ago. Zulip has 25,921 stars, 10,247 forks, 2,008 open issues and last shipped yesterday. cobalt leads on adoption by 67% (43,316 vs 25,921 stars). cobalt is written in Svelte under AGPL-3.0; Zulip is written in Python under Apache-2.0. cobalt has attracted 9% as many forks as stars, Zulip 40%. Zulip was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 2 topic tags (collaboration, javascript), 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
| cobalt | Zulip | |
|---|---|---|
| GitHub stars | ★ 43K | ★ 26K |
| License | AGPL-3.0 | Apache-2.0 |
| Written in | Svelte | Python |
| Last push | 2026-04-06 | 2026-09-17 |
| Forks | ⑂ 3.8K | ⑂ 10K |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick cobalt if
- You weight community size — 43K stars and counting
- You want the AGPL-3.0 license terms
- Your stack matches Svelte
- You value the larger contributor base for long-term maintenance
pick Zulip if
- You want the Zulip feature set and don't need the biggest community
- You prefer the Apache-2.0 license terms
- Your stack matches Python
- You evaluated both and Zulip fits your workflow better
About cobalt
cobalt is a media downloader built around a single promise: paste a link, get the file, move on. It is a monorepo containing the source for an API, a web frontend, and related packages, written primarily in Svelte and TypeScript. The project lives in the modern web and JavaScript ecosystem, and its public surface is hosted at cobalt.tools, while the full codebase is published under the AGPL 3.0 license.
read the full cobalt overview →
About Zulip
Zulip is an open source organized team chat application built on topic based threading, aimed at distributed teams that need live and asynchronous conversation in one place, and it is positioned as an open alternative to Slack.
read the full Zulip overview →
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Frequently asked questions
Is cobalt or Zulip more popular?
cobalt has 43,316 GitHub stars and Zulip has 25,921. cobalt has the larger community by that measure.
Are cobalt and Zulip free?
Both are open source. cobalt is licensed under AGPL-3.0 and Zulip under Apache-2.0. Neither carries a licence fee.
What is the difference between cobalt and Zulip?
cobalt is written in Svelte and Zulip in Python. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, cobalt or Zulip?
Choose cobalt if you want the larger community (43,316 stars) or its AGPL-3.0 licence terms. Choose Zulip if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.