Xamarin now provides a single API for both Mac OS and iOS for 32-bit and/or 64-bit.
In order to support 64-bit iOS and OSX, Xamarin has to make some breaking changes to the way it implements the mapping between C# and Objective-C libraries. Rather than being mapped to 32-bit types, NSInteger and CGFloat are now mapped to the new platform-specific data types nint and nfloat.
Xamarin has released a preview of their async-enabled libraries for iOS and Android development. This work is based heavily on Microsoft’s .NET 4.5, which was released late last year as part of Visual Studio 2012. Xamarin is the new name for the development platforms previously known as MonoTouch and Mono for Android.
Xamarin has made yet another major step in completing their vision on providing a set of common tools for cross-platform mobile development. With the announcement of Xamarin 2.0 comes a rebranding of their products, a new IDE called Xamarin Studio, a Visual Studio add-in for iOS development, and a component store, the later being detailed by Miguel de Icaza for InfoQ.
Xamarin, makers of the popular MonoTouch and Mono for Android platforms, have entered into the Mac App Store market with Xamarin.Mac.