Xamarin - Free. Cross-platform. Open source.
.NET is a developer platform made up of tools, programming languages, and libraries for building many different types of applications.
Xamarin apps are native apps! Whether you're designing a uniform UI across platforms or building a native user interface, your apps will behave the way users expect.
Xamarin is part of the vibrant .NET ecosystem, used by millions of developers worldwide. Share more than 75% of your code across platforms, for "write once, run anywhere" ease.