Google Wave is the new phenomenon.
You can check out on the harp here.... https://services.google.com/fb/forms/wavesignup/.
You have to get from them only, unlike the mail invite from Google. ( old days Beta style! )
Well what are the features with Wave?
hmm.. dunno. Everyone talks and tweets about it.
Why don't you check out on this http://pygowave.net/blog/