Microsoft on Monday released a software development kit for Facebook that allows developers to create Facebook applications for Silverlight and Windows Presentation Foundation. This should expand the reach of Facebook in third-party applications as well as make Silverlight and WPF more viable platforms for developers looking to build social applications.

The SDK comes complete with samples and tools to develop Facebook applications in ASP.NET, Silverlight, WPF, and WinForms. It also features the source code for the API, components, controls, and samples.

There are currently other libraries available that allow Facebook developers to develop with other technologies, such as JavaScript, PHP, ActionScript, and the iPhone. There are a variety of others as well, which can be seen here, but these are the ones that Facebook officially provides support for.

Microsoft, as you may remember, invested $240 million in Facebook back in October 2007. Many called this move more of a strategic play to keep Google and Yahoo from getting a stake in the company. The release of this SDK is a part of Facebook and Microsoft's ongoing partnership.

If you're interested in taking a look, you can download the SDK here.