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: 5.13.1

Requirements: macOS >= 11

Versions:

Intel tahoe 5.13.1
sequoia 5.13.1
sonoma 5.13.1
ventura 5.13.1
monterey 5.13.1
big sur 5.13.1

Analytics:

Installs (30 days)
mattermost 373
Installs (90 days)
mattermost 1,089
Installs (365 days)
mattermost 4,787