Xamarin

Owned by Microsoft, Xamarin is an open-source platform for building hybrid mobile apps using .NET and C#. It offers excellent native user interface, which helps developers to build native apps with amazing user experience. All this is achieved with Xamarin's flexible .NET dev platform which is loaded with varieties of tools & an in-depth library for building apps for Android, iOS, tvOS, watchOS, macOS, and Windows. Xamarin also offers good customer support as it is registered under a major brand i.e, Microsoft.