Google Shared Spaces, is a small Google Labs project that helps you collaborate with other people by adding information to a gadget. You can add placemarks to a map, draw on the same white board, play Sudoku, create lists, find the best budget accommodation, brainstorm, create diagrams and answer to polls.
Maybe Google Wave would've been more successful if it didn't have so many complicated features and ambitious goals. Google Wave could've been the back-end technology for many cool web apps, instead of trying to incorporate all the use cases in a single interface.
More Info: Gogle Shared Spaces