Slack is the de facto standard for team communication, but its free plan has become increasingly restrictive. The following open source alternatives can be self-hosted with no message history limits. Mattermost offers the easiest migration from Slack, Rocket.Chat is feature-rich, and Zulip is known for its threaded UI.
4 tools
Rocket.Chat
45,077TypeScriptNOASSERTION
The Secure CommsOS™ for mission-critical operations
Open CoreJapanese UI
mattermost
36,060TypeScriptNOASSERTION
Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
Open CoreJapanese UI
zulip
24,984PythonApache-2.0
Zulip server and web application. Open-source team chat that helps teams stay productive and focused.
Open CoreJapanese UI
element-web
12,941TypeScriptAGPL-3.0
A glossy Matrix collaboration client for the web.
FreeJapanese UI