Riot : Riot allows teams to communicate across a wide range of collaboration apps. If some team members use Riot while others use IRC, Slack or Gitter, Riot ...
Zulip : Powerful slack-like open source group chat
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 ...
ProjectPier.org : ProjectPier is a Free, Open-Source, PHP application for managing tasks, projects and teams through an intuitive web interface. It must be downloaded a...
Lemmy : Lemmy is a selfhosted social link aggregation and discussion platform. It is completely free and open, and not controlled by any company. This means t...
Mattermost is a self-hosted solution for bringing all your team communication to one place, and making it searchable and accessible anywhere