Open source Slack alternative from Block: team chat with AI agents as first-class members, built on Nostr. Apache-2.0. 3 days old, still rough at the edges.
You pay for Slack
There is an open source for Slack
2 reviewed open source alternatives to Slack. Each carries a source and a date. Pick the one that fits how you work.
Open-source team chat with topic-based threading for live and async work. Paid Zulip Cloud or self-host on Ubuntu, Debian, and Docker.
"The channel as memory has been a big help on larger features that span multiple engineers and many agent sessions. Someplace ad-hoc that's shared makes a real difference."
"I've used Zulip. It's a cool idea, though it turned out to be still too beta to replace HipChat at my company. The key feature is having multiple threads of conversation in one room..."
| Project | License | Stars | Last release | Hosted | Docker | Zero terminal | Install path |
|---|---|---|---|---|---|---|---|
| Buzz | Apache-2.0 | 26.3k | 2026-08-10 | Yes | No | Yes | Install path |
| Zulip | Apache-2.0 | 25.6k | 2026-08-10 | Yes | Yes | Yes | Install path |