ExEn, if you haven’t heard, is my port of XNA to Silverlight and iOS (and coming soon to Android and possibly Mac OS X). The pre-release program for ExEn has been open for a month now, and some of the people in the program are already using ExEn to develop games!
ExEn is a fantastic way to port your XNA game to Silverlight and iOS, with very little need for code changes (similar to porting between Windows, Xbox 360 and Windows Phone 7, within XNA). It also allows you to leverage the power of XNA and C# for making Silverlight and iOS games.
If you would like to start using ExEn right away, join the pre-release program. ExEn is currently in development, but the Silverlight and iOS versions are complete and stable enough to use in production work. Work on the Android port will be commencing very soon.
For more information visit http://AndrewRussell.net/exen/