I'm not sure what to make of Google Wave just yet.  It seems to me like it's a collaboration tool more than anything - you'll be able to share and create documents with rich text and multimedia support, and these projects are updated real time to allow easy communication between participants.  Still, there is Google inbox, chat and Picasa integration, and it's been said that this is Google's response to Twitter.  Based on the screenshots it looks like it'll be a good way to communicate with friends, but the description makes Wave sound like something entirely different.  All I know is that I like the user interface, and I'm happy it's open to developers.

You can throw your name into the hat to try Google Wave as soon as it becomes available at the link below.

http://wave.google.com/

Google Wave Preview screenshot