Xamarin.iOS (previously known as MonoTouch) is a commercial software development kit for Mac OS X and Windows that lets you use C# (a .NET programming language) to create native applications for Apple iPhone, iPod Touch, iPad (iOS), Apple Watch (watchOS) and AppleTV (tvOS) devices.
Xamarin.iOS (previously known as MonoTouch) is a cross-platform implementation of Microsoft's CLI (.NET) that lets developers write "once" for iOS, OS X, Android, and Windows Phone in C#.
Xamarin comprises an IDE (Xamarin Studio for OS X and Windows), a plugin for Visual Studio, and libraries for each of the target OS's. Xamarin implements a hybrid approach to cross-platform development, whereby business logic exists in a shared core project, and the visual layer is implemented in platform-specific projects for each target platform.
Developers thus have access to advanced C# language features and libraries, as well as platform-specific UI libraries. To comply with Apple policy, iOS and OS X apps compile "all the way out" so as not to require a runtime.
