Google Wave is a web based communication system accessed through your browser. It allows users to create a new "Wave" where any topic can be discussed. In the wave you can add new text, edit others notes, add images, map info, and tweets. The wave allows real time updates from multiple people and multiple sources.
Wave.Google.com is the home page and they have a video presentation posted.
The video/presentation is long and 1hr 20 minutes. At the end they show some cool extensions that have been built. http://wave.google.com/ If this catches on it could put a real dent in the Basecamp Market.
I would love to hear others thoughts about Google Wave.