Xamarin allows developers to build native iOS, Android, and Windows apps using C# and .NET while leveraging rich IDE support like Xamarin Studio and Visual Studio. It offers streamlined design, development, debugging and deployment of mobile apps with native UI and performance. Developers can also access a component store to add third-party libraries and UI controls with a few lines of code. Xamarin provides a free starter edition for small businesses and individual developers to get started building mobile apps.