Rocket.Chat
Self-hosted team messaging — channels, video, and compliance.
MIT-licensed alternative to Slack and Mattermost with end-to-end encryption, Omnichannel, apps marketplace, and FedRAMP-ready compliance.
Zulip
Topic-threaded team chat — keeps conversations organized at scale.
Zulip is an open-source team chat application built around topic-based threading, which keeps conversations organized in a way that channel-only tools like Slack or Rocket.Chat don't. Apache-2.0 licensed and self-hostable.
Compare Mattermost alternatives
| Tool | Stars | Forks | License | Self-hosted |
|---|---|---|---|---|
| Rocket.Chat | 45.4K | 13.6K | MIT | Yes |
| Zulip | 25.5K | 9.9K | Apache-2.0 | Yes |
Mattermost is itself open-core team collaboration software — the Team Edition is free and self-hostable, with advanced features reserved for the paid Enterprise Edition. So this comparison is less about proprietary lock-in and more about which self-hosted chat platform's free tier covers what your team actually needs.
If Mattermost's Enterprise-gated features (like advanced compliance or SSO) are a blocker on the free tier, Rocket.Chat is worth comparing since it draws that line differently, with omnichannel support (SMS, WhatsApp, email) included in its free plan.
FAQ
Is there a free, open-source alternative to Mattermost?
Mattermost's Team Edition is already free and open source. If you want a different open-source option, Rocket.Chat is a widely used alternative with broader free-tier channel support.
What's the best open-source alternative to Mattermost?
Rocket.Chat is the better pick if you need omnichannel messaging (SMS, WhatsApp, email) in the free tier, which Mattermost reserves for paid Enterprise Edition.
What are the top open-source alternatives to Mattermost?
Browse all open-source alternatives to Mattermost above, or explore the full Communication & Community category for more options.