Rocket.Chat
Rocket.Chat is an open source project for team communication. This software is a free alternative for other chat programs like Slack.
The SIC is hosting a Rocket.Chat instance for members of the SIC.
It can be accessed at: https://rocketchat.cs.uni-saarland.de
There are also desktop and mobile clients available:
https://rocket.chat/docs/installation/mobile-and-desktop-apps/