Rocket.Chat : Rocket.Chat is a Web Chat Server, developed in JavaScript, using the Meteor fullstack framework.
It is a great solution for communities and companies ...
WorkAdventure : Stay connected with your co-workers, by creating your own online workspace to work remotely.
Gather : Spend time with your friends, coworkers, and communities like you would in real life
YunoHost : YunoHost is a server operating system aiming to make self-hosting accessible to everyone.
Imagine all your team communication in one place, instantly searchable, available wherever you go. That's Slack.