HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
Shtuff Chat - Free Group / Team chat with persistent history.
Slack - A messaging app for teams who see through the Earth!
Meet in Chat - Meet new people. Have fun sharing photos.
Skarpline - Skarpline provides centralized enterprise messaging, link sharing and file management to improve productivity.
Kandan - Open Source private chat server. Your own private Chat server in minutes, plus additional features.