mattermost

Install command: 
brew install --cask mattermost

Name: Mattermost

Open-source, self-hosted Slack-alternative

https://mattermost.com/

Cask JSON API: /api/cask/mattermost.json

Cask code: mattermost.rb on GitHub

Current version: 6.0.1

Requirements: macOS >= 12

Versions:

Intel tahoe 6.0.1
sequoia 6.0.1
sonoma 6.0.1
ventura 6.0.1
monterey 6.0.1

Analytics:

Installs (30 days)
mattermost 438
Installs (90 days)
mattermost 1,149
Installs (365 days)
mattermost 4,822