About a week ago, Google released a preview version of a program called Google Wave. It's described as a "personal communication and collaboration tool".
Google Wave Homepage
You've all used Email, Facebook, AIM/ICQ/MSN, and maybe edited a few Wikipedia entries in your time. Google Wave combines the features and experiences of all of these into one program. Once I get a chance to try it for myself, I will be sure to post here about it
Web 2.0 include web-based communities, hosted services, web applications, social-networking sites, video-sharing sites, wikis, blogs, mashups, and folksonomies. A Web 2.0 site allows its users to interact with other users or to change website content, in contrast to non-interactive websites where users are limited to the passive viewing of information that is provided to them.