[kevingadd]

The C# tooling is good but it's partially closed-source and sold by a vendor (Xamarin). On that basis I don't think it really 'counts'. JS does, at least, since there are many ways to ship JS-based Android apps for free.

[Maarten88]

Xamarin got bought by Microsoft, and they opened almost everything from Xamarin, except Xamarin Studio which got rebranded as Visual Studio for Mac.