Open Source Slack Alternative | Mattermost
https://mattermost.com/open-source-slack-alternative/
WebMattermost is the only open source collaboration platform that gives you the ability to customize, extend, and build bespoke integrations — including legacy systems. 25,000+ GitHub™ Stars. 30,000+ total contributions. 4,000+ contributors. The OSS CommunityMattermost. More deployment options than Slack.
DA: 35 PA: 12 MOZ Rank: 83