A port of XNA has been released in its first public preview and is named ExEn. It's not officially supported by Microsoft, but it was created by an individual named Andrew Russell. The port runs on Silverlight and iOS, but an Android version is in the works. For those who may not know, XNA is a set of tools written by Microsoft that facilitates computer game development. The framework runs on .NET Compact Framework 2.0 for Xbox 360 and .NET Framework 2.0 for Windows. Since the XNA technology is licensed under the MS-PL (Microsoft's open source licensing), you can start using ExEn in games right away.
Its worth noting that the iOS version uses a port of .NET Framework called MonoTouch. It was developed by Novell. In addition, ExEn does conform with Apple's restrictions, so games for iOS devices will be permitted in the iTunes App Store, as long as the games follow the other restrictions applicable to games. It is also important to note that ExEn has been delayed several times. Those who donated to the project before this past Wednesday will be given special access to the prerelease program. You can also donate via Andrew Russell's site if you wish. The download link for the public preview of ExEn is here. Sound off in the comments if you test this program.