HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
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.
Rivers IM - Simple, fast & secure team collaboration platform
Chatib - Chatib is an online chat room where you can meet and chat with new people, make them friends, or even data them online.
Slack - A messaging app for teams who see through the Earth!
Kandan - Open Source private chat server. Your own private Chat server in minutes, plus additional features.