Xamarin is a cross-platform mobile development framework available within the Visual Studio IDE utilizing .NET's cross-platform functionality. Android apps are bundled and distributed with the MonoVM enabling .NET code compiled into Intermediate Language to run on an Android device. IOS apps are compiled into ARM assembly language courtesy of Xamarin libraries. They can be debugged on an iOS device plugged into your computer or on a Mac running a simulator using Xcode. As Xamarin is a .NET technology, apps are written primarily using C#, although F#, a .NET functional programming language, is also an option. 

A Visual Studio Xamarin solution is made up of multiple projects. The Xamarin project, where most of the codebase resides, and a project for each targeted platform. The platform-specific projects will become the apps, with each referencing the Xamarin project for the shared codebase. A Xamarin forms project enables you to develop a shared user interface, defining graphical screen elements with XAML – the extensible application markup language. While Xamarin forms apps ensure the most shared code and reduced development time, they aren't as performant as native apps. Xamarin native apps only share the business logic or non UI codebase. The apps' user interface is defined within each platform-specific project. This means more time in development, but native UIs have access to all of the device's functionality, and in the case of iOS, Xamarin native apps' performance is on par with purely native apps.

In this course, we've looked at how Xamarin's architecture tackles sharing a codebase in a cross-platform scenario. We've seen how to set up a Xamarin development environment on Mac and Windows machines and what's involved in building and debugging simple Andriod and iOS applications.