brad johnson
brad johnson reviewedRocket.ChatYour own open source Slack-like chat
 RecommendedPros: 

Easy to install. Group chat and encrypted chat. Integrations and bot support.

Cons: 

It is almost the same as Slack but you can install it on your own system.

I got it to run on an Raspberry Pi https://volumeintegration.com/installing-rocket-chat-on-raspberry-pi-2/

brad johnson has used this product for one year.