Slack - A messaging app for teams who see through the Earth!
Tlk2me - Tlk2me is simple real-time messaging platform which is designed exclusively for groups.
Rizzoma - Email and IM are linear contextless communication tools.
Collaba - Collaba is an easy-to-install, double-click-to-run, server software that provides integrated services such as: e-mail, calendaring, files & documents, assignments, blogs, multimedia chat, forums, bookmarks, web publishing, wiki, single sign-on, LDAP…
Walkaround - Walkaround is a variant of Wave, based on the Apache Wave code base, that runs on App Engine.
Unsee - The ability to open a chat session and message then delete it from history forever just like tlk.