Open-source alternatives to Slack
Looking to replace Slack with something free and open-source? These 3 tools are the best open alternatives in 2026 — most are self-hostable, so you keep full control of your data and pay no subscription.
At a glance: how they compare
Click a column to sort — the best one depends on what matters to you.
| Alternative | Stars | Language | License | Last commit | In one line |
|---|---|---|---|---|---|
| Mattermost | — | — | MIT / AGPL | — | Self-hosted team messaging built for security-conscious orgs. |
| Rocket.Chat | — | — | MIT | — | Full team-collaboration platform you can host yourself. |
| Zulip | — | — | Apache-2.0 | — | Threaded team chat that keeps conversations organized. |
Which one should you pick?
Mattermost
Self-hosted team messaging built for security-conscious orgs. Its MIT / AGPL license keeps the project and its forks open-source forever, and commercial use is allowed. Because it is self-hostable, your data can stay entirely on your own infrastructure.
Rocket.Chat
Full team-collaboration platform you can host yourself. Its MIT license is permissive — free to use commercially, embed and modify. Because it is self-hostable, your data can stay entirely on your own infrastructure.
Zulip
Threaded team chat that keeps conversations organized. Its Apache-2.0 license is permissive — free to use commercially, embed and modify. Because it is self-hostable, your data can stay entirely on your own infrastructure.
Switching from Slack without the drama
- Export your data from Slack first — most tools above can import standard formats.
- Run your top pick in parallel for a week or two before committing; self-hosted options can be tried locally in minutes.
- Migrate one team or one project at a time, keeping the old account read-only until everything checks out.
FAQ
What is the best open-source alternative to Slack?
The top open-source alternative is Mattermost — Self-hosted team messaging built for security-conscious orgs. The full ranked list is above.
Are these Slack alternatives free?
Yes. Every tool listed is open-source and free to use; most can be self-hosted so you keep full control of your data.
Can I self-host an alternative to Slack?
Most of these tools are designed to run on your own server or machine, giving you privacy and no subscription fees.
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