mattermost

Install command: 
brew install --cask mattermost

Name: Mattermost

Open-source, self-hosted Slack-alternative

https://about.mattermost.com/

/api/cask/mattermost.json (JSON API)

Cask code on GitHub

Current version: 4.7.0

Analytics:

Installs (30 days)
mattermost 319
Installs (90 days)
mattermost 1,139
Installs (365 days)
mattermost 5,005
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