Open source Slack alternative
Twake 2.0
The open source alternative to Slack,Trello,Drive and Teams
Total.js Messenger
A small, open-source alternative to Slack
Rocket.Chat
Your own open source Slack-like chat
Linen Community
Free open source Slack alternative for communities
Slack Vibe 🎉
Open source analytics for Slack
Mattermost
Open source, on-premises, Slack alternative
Mattermost 1.0