HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
Waver - Description: Google Wave is a great way to communicate and collaborate. Waver lets you:
Slack - A messaging app for teams who see through the Earth!
Rizzoma - Email and IM are linear contextless communication tools.
Skarpline - Skarpline provides centralized enterprise messaging, link sharing and file management to improve productivity.
BSI Knowledge Manager - Central document management & knowledge base