http://wave.google.com

Google Wave is an online tool for real-time communication and collaboration. A wave can be both a conversation
and a document where people can discuss and work together using richly formatted text, photos, videos, maps, and more.

What is a wave?

A wave is equal parts conversation and document. People can
communicate and work together with richly formatted text, photos,
videos, maps, and more.

A wave is shared. Any participant can reply anywhere in the message,
edit the content and add participants at any point in the process.
Then playback lets anyone rewind the wave to see who said what and
when.

A wave is live. With live transmission as you type, participants on a
wave can have faster conversations, see edits and interact with
extensions in real-time.

Some key technologies in Google Wave

Real-time collaboration
Concurrency control technology lets all people on a wave edit rich media at the same time.

Natural language tools
Server-based models provide contextual suggestions and spelling correction.

Extending Google Wave
Embed waves in other sites or add live social gadgets, thanks to Google Wave APIs.

Even though you have a Gmail or a Google account, you must be invited to Google Wave in order to sign in. If you haven’t been invited by a friend, you won’t be able to use the service at this time.

If you have been invited, but you aren’t able to sign in, make sure you follow the link in the email invitation the first time you want to access the service. You must use your unique URL the first time you sign in to Google Wave.

Google Wave is currently available in a limited preview release. Sign up to receive updates about Google Wave’s availability.