Unsee - The ability to open a chat session and message then delete it from history forever just like tlk.
Walkaround - Walkaround is a variant of Wave, based on the Apache Wave code base, that runs on App Engine.
Chatango - Add free live chat to any web page. Chatango is a live group on your site
Rizzoma - Email and IM are linear contextless communication tools.
Slack - A messaging app for teams who see through the Earth!
Waver - Description: Google Wave is a great way to communicate and collaborate. Waver lets you: