Xamarin is a San Francisco, California based software company created in May 2011 by the engineers that created Mono, MonoTouch and Mono for Android which are cross-platform implementations of the Common Language Infrastructure (CLI) and Common Language Specifications (often called Microsoft .NET).With a C# shared codebase, developers can use Xamarin tools to write native iOS, Android, and Windows apps with native user interfaces and share code across multiple platforms.