Vanilla Forums - Build an engaging community forum using Vanilla's modern cloud forum software.
Slack - A messaging app for teams who see through the Earth!
Forumbee - Forumbee offers community forums for discussions, feedback and Q&A.
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
Mattermost - Mattermost is an open source alternative to Slack.