Google Wave (currently in preview) is a new online collaboration tool created by Google. It provides the opportunity for asynchronous and synchronous communication among users. Waves allow participants to share resources, images, videos, documents, etc in order to discuss, collaborate, etc. It's a wonderful tool and my guess is that it will only become more powerful when it is open to all and a little more polished. Even in it's current state, it's quite robiust.