“Google Wave is a new tool for communication and collaboration on the web, coming later this year.”
but words don’t do it justice. You should watch the video for various demo of wave. I can see myself using my email, calendar and documents tools less and less… and eventually I can see wave replacing them for good. (if everybody gives up control to the all mighty google that is 
)
If there is something it doesn’t do, you can extend it by writing your own server bot or client side widget that will.
If you haven’t checked out Google Wave, you should at http://wave.google.com/