Facebook today released the Facebook SDK for .NET, to enable Windows-focused developers to integrate their applications with Facebook.
The SDK was announced on the Windows Phone Developer Blog. The open-source SDK is C#/XAML based, and can be found at the Outercurve Web site. Most developers will want to install the SDK using NuGet (this page recommends having the latest version of NuGet; some features of the SDK won’t work with older versions.)