Open-source alternatives to Slack

Team messaging platform with channels, threads and app integrations.

4 open-source swaps125k GitHub stars between them

The open-source options, most starred first

Read from GitHub. Check the licence and what each one covers before you switch.

The Secure CommsOS™ for mission-critical operations

Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..

Zulip server and web application. Open-source team chat that helps teams stay productive and focused.

A glossy Matrix collaboration client for the web.