Many developers want to try their hand at writing an iOS application. The big drawback has always been learning a new programming language and a new IDE. For some, it is probably not an issue as they want to learn something new. But for many .NET developers, being able to stick to an IDE and programming language they know is immensely empowering. Well, this is exactly what Xamarin Forms and Visual Studio achieve. It gives .NET developers the ability to use Visual Studio to write applications that can be run cross-platform easily, without having a separate code base for each.
You will need to have a Mac running OS X. You will only need this for debugging iOS applications.