Team chat · Updated October 2026
Slack is a team chat app built around channels, direct messages, and integrations. If you would rather own your tools, here are 5 open source alternatives to Slack, ranked by GitHub stars. Each one is free to use under its license, and you can read, change, and often self-host the code.
Rocket.Chat is both the most popular, with 46.3k stars, and the most recently updated, with a commit on Oct 21, 2026.
| Project | Stars | License | Language | Last commit |
|---|---|---|---|---|
 Rocket.Chat | 46.3k | Other | TypeScript | Oct 21, 2026 |
 Mattermost | 39.4k | Other | TypeScript | Oct 21, 2026 |
 Huly | 28k | EPL-2.0 | TypeScript | Oct 19, 2026 |
 Zulip | 26.1k | Apache-2.0 | Python | Oct 21, 2026 |
 Element | 13.6k | AGPL-3.0 | TypeScript | Oct 21, 2026 |
by RocketChat
The Secure CommsOS™ for mission-critical operations
by mattermost
Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
by hcengineering
Huly — All-in-One Project Management Platform (alternative to Linear, Jira, Slack, Notion, Motion)
by zulip
Zulip server and web application. Open-source team chat that helps teams stay productive and focused.
by element-hq
A glossy Matrix collaboration client for the web.
By GitHub stars, Rocket.Chat is the most popular open source alternative to Slack right now, with 46.3k stars, followed by Mattermost and Huly. The best fit depends on your setup, so compare their licenses, languages, and recent activity in the table above.
Yes. All 5 projects on this page are open source, so the software itself is free to use, study, and change. Some of them also sell a hosted version or paid support.
Rocket.Chat (last commit Oct 21, 2026), Mattermost (last commit Oct 21, 2026), and Element (last commit Oct 21, 2026) have the most recent commits. Licenses on this list include EPL-2.0, Apache-2.0, and AGPL-3.0.
