Scott Guthrie, VP of Microsoft's Developer Division, originally demonstrated a Silverlight client for Facebook during his PDC 2009 keynote late last year.
Today Microsoft has made the Silverlight Client available for Windows and Mac OS X users to install. The client requires Silverlight 4 and installs a simple link to the web version which loads in its own window. As is expected with Facebook clients, you can see a full time line from your feed, pictures, video and Facebook notifications. You're also able to drag and drop pictures to easily share with Facebook friends.
Microsoft has also added the ability to take pictures from your webcam. According to Microsoft's Tim Heuer "The Facebook client is meant to be a working demonstration/inspiration of what one could do with existing services and providing different views into an existing application framework." Microsoft officials also confirmed no source code would be made available initially for the application. The application is also similar to what Microsoft demonstrated in April last year, originally named "Silverface".
Microsoft also released a Windows 7 Facebook client named "Fishbowl" in November 2009. Fishbowl also includes Windows 7 only features, including taskbar notifications, jump-lists and taskbar previews
Download: Silverlight Client for Facebook