Pibb is a GWT based web app that tries to combine the best features of IM, email, chat and message boards.

• Messages are delivered instantly, or can be retrieved later
• New threads are stored and searchable like email or bulletin board
• Start public channels about your favorite subjects
• Use private channels to communicate with groups or your social network
• Send private messages to your friends
• Pibb will notify you when you have new messages

It supports OpenID so I was able to try out the app using my AIM login, so no registration necessary. The interface looks really nice and so far has been pretty intuitive. I hope people check it out.