Open-source alternatives / Slack
Mattermost — free open-source Slack alternative
39,247 GitHub stars
Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
Replaces: Slack — the paid alternative. Mattermost does the same job and the licence is $0: you pay only for the server it runs on.
Why teams switch to Mattermost
- $0 licence. The paid tool charges per seat every month. Mattermost is free forever, including commercial use under its open-source licence.
- Your data stays yours. Mattermost is self-hosted — it runs on your own server, so no third party holds your records.
- Proven at scale. 39,247 GitHub stars and an active contributor base mean real companies run this in production, not just hobbyists.
Trade-off, honestly: open-source means you (or an IT person) install and maintain it. If nobody on your team can run a server, the paid alternative may still be the right call — that is what it is charging for.