UPDATE: Google Wave has been discontinued.
Google wave is Google's next wave (eh?) of online collaboration and communication service. It is touted to be open source, and thus opening up a lot of possibilities for enhancements and features. In a nutshell (at least, from what I can gather from the 1+ hour youtube video presentation I have partly watched) , Google Wave is a mixture of chat and email with a whole lot of media capability built in. A "wave" is basically a conversation thread in which people included in the group can add comments and rich content anywhere in the timeline. And even if you have just joined the wave long after it was created, you can "turn back time" and see how the wave progressed and insert your own content into, well, anywhere you please onto the wave. Groovy, eh?
Google Wave is still in its early development and some lucky folks were able to get invitations to test (just like Google Mail in its early stage). If you scour the net for news about Google Wave, you would get mixed reactions but it's still too early at the onset to see what it will evolve into. But still, you gotta love the way Google innovates.