A few weeks back, Microsoft released the Windows Live Messenger Facebook Application. Members of Facebook can chat with their friends using this application that runs on the Facebook site.
The application also shows the WL Messenger online presence of your Facebook friends who have installed the application (it is based on the Windows Live Messenger Presence API)
Currently its only available in English but can run in all facebook sites.
Essentially any Facebook user can add this application to his/her Facebook profile page. It allows people who have access to his/her Facebook profile page, regardless of whether or not they use Windows Live Messenger, to see what his/her WL Messenger presence is and to start IM conversation with him/her through the Windows Live Messenger service (it is based on the Windows Live Messenger IM Control which allows anonymous chat).
Will post more on its showing at Mix where we saw the ability to interact with a television show and talk to your friends about it via messenger (all on one window)