Mattermost is an open source, private cloud, Slack-alternative from https://mattermost.com.
It's written in Golang and React and runs as a single Linux binary with MySQL or PostgreSQL. Every month on the 16th a new compiled version is released under an MIT license.
Try out Mattermost
Deploy on Heroku
Note: Heroku preview does not include email or persistent storage
Auto-deploy Mattermost to Amazon Web Services, Azure, Google Cloud Platform, or Oracle Cloud Platform via Bitnami.
Install on Your Own Machine
Native Mobile and Desktop Apps
In addition to the web interface, you can also download Mattermost clients for Android, iOS, Windows PC, Mac OSX, and Linux.
Get Security Bulletins
Receive notifications of critical security updates. The sophistication of online attackers is perpetually increasing. If you are deploying Mattermost it is highly recommended you subscribe to the Mattermost Security Bulletin mailing list for updates on critical security releases.
Get Involved
Learn More
Get the Latest News
Any other questions, mail us at info@mattermost.com. We’d love to meet you!