One of the big wins for C# developers with the announcement of collaboration between Microsoft and Xamarin is that Portable Class Library (PCL) projects are now fully supported on both iOS and Android, making it easier than ever for C# developers to share code across devices. What this also means is that your existing .NET apps can be easily ported to mobile by moving the code that is platform agnostic to a portable class library that can be referenced from iOS, Android, Windows Phone, and Windows Store projects. Almost any .NET codebase, including Windows Forms, WPF, ASP.NET, and Silverlight, has sharable code that can be ported to Xamarin.iOS, Xamarin.Android, Windows Phone & Windows Store.
Read more: Xamarin