If you mean what languages have a near Flash equivalent API, then Dart has StageXL

http://www.stagexl.org

Hmm, hadn't heard of that one before.

I don't think there's a drop-in alternative to the Flash API other than OpenFL, but you can achieve the same outcomes in pretty much any language.

If you're just looking for multi-platform stuff, that's almost a minimum requirement now: unity3d, unreal engine, xamarin, javascript etc.

unity/unreal engine isn't really a fair comparison, you're either requiring a web view plugin (unity), or you're going with emscripten (unity/unreal). I couldn't find evidence of solid support for Xamarin there either.

Haxe has the ability to integrate much more cleanly across all of these platforms imho.