Rizzoma - Email and IM are linear contextless communication tools.
Walkaround - Walkaround is a variant of Wave, based on the Apache Wave code base, that runs on App Engine.
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…
Slack - A messaging app for teams who see through the Earth!
Jostle - A new kind of employee intranet that drives engagement & workplace culture. Achieves social participation in work relevant way. Participation rates are over 85%.
Tlk2me - Tlk2me is simple real-time messaging platform which is designed exclusively for groups.