Silverlight runs on Windows, MAC, Linux (via Moonlight Project),Winodws Phone 7, Nokia Symbian S60 Phones, Set Top Boxes, XBox
What is Silverlight?
Silverlight is a cross-platform .NET runtime, cross-browser plug-in, and a set of Windows-based developer tools for building RIAs. At its heart, Silverlight is an implementation of the concepts and standards from Windows Presentation Foundation (WPF) such as binding, the property system, and Extensible Application Markup Language (XAML) in a crossplatform version of the .NET Common Language Runtime (CLR) and libraries.
Microsoft Releases Minesweeper For WP7
Silverlight 5 RC released
Silverlight 5 RC Released and could be downloaded at http://www.silverlight.net/downloads