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.
Watch some tech videos and get more information from here: About Google Wave
Currently, Google Wave is invite only. I hope to receive an invite by tonight, so will be able to give my opinion only then. If someone else has already had the invite and have been using this, put down your views here.
EDIT:
Some more info can be had here: Google Wave - Wikipedia, the free encyclopedia
Google plans to make most of this as open source, so we can expect more features to be added in the form of plugins or extensions.