Microsoft released a Facebook SDK to make it easy for .NET devs to use Facebook Open Stream API. This toolkit’s provided as a Facebook Client Library similar to Facebook's PHP Client Library or Facebook's JavaScript library. The goal’s to enable .NET developers to quickly and easily leverage various features of Facebook Platform. The SDK supports apps in Silverlight, WPF, ASP.NET, ASP.NET MVC, and Windows Forms. Windows Developer Center has download, how-to guides, a wiki, and sample code to get you started.

Download: Facebook SDK | How To Guides