Kotlin has been a joy to use. Really happy with it. Our Android app ( http://play.google.com/store/apps/details?id=com.eatsa.app ) is 100% Kotlin (with a good amount of Java libraries of course). Some highlights: - Great type system, with type inference. - Full Java interop. You can literally copy/paste Java code from Stackoverflow and it's automatically translated to Kotlin. It doesn't feel like 2 different language…
Why not use Xamarin? it has a better lenguaje (C#) and is free.
Apps written in Xamarin and kotlin work very differently :
-with Xamarin you have to add the Xamarin runtine and depend on its integration. This brings several downsides : http://www.slideshare.net/KonstantinLoginov/we-are-ditching-...
-Kotlin outputs bytecode, so from the outside, it is just the same as any android app written in java. The output is a standard android app with one more library (the standard kotlin lib with all its base methods)