Google Wave was a great idea I felt. We adopted it at work for collaborative discussions and found it a better way to communicate than just IM and Email. Sadly, Google have decided not to continue developing the application.
However, as announced yesterday, Google are going to Open Source more of the Wave code and even bundle many of the elements into a complete solution.
I will be following this as Wave and Etherpad and co are really execllent tools with a lot of potential.