What is Google Wave ?
Google Wave is a new communication and collaboration platform based on hosted XML documents (called waves) supporting concurrent modifications and low-latency updates. Google Wave is an HTML 5 app, built on Google Web Toolkit.
Google wave has lot of features where you can communicate easily using Google wave. Most of the time mail and instant messaging are done sepeartely but Google wave makes communication in a single platform. You can watch what your friend is typing simultaneously in chat, which makes communication more faster.
More info : http://wave.google.com
15 cool features: http://www.youtube.com/watch?v=xBzuuWZPaXc
Edit: If you need Invitation , comment to this post with your email id. I will send a invation . Hurry up. Only limited available.