BuddyFuse integrates third party (social / IM) networks into Windows Live Messenger. By doing this you can chat with your friends on those social networks from Windows Live Messenger, so no need to go to these networks anymore just for a chat. Currently it is available in beta, only supporting the Dutch social network Hyves. They do plan on integrating other social networks too, like Facebook, Google Talk (GMail chat) and Twitter.
More info: BuddyFuse