The article also links to Haxe. It looks like Haxe does not come with a cross-platform UI framework, but there are some projects that appear to do just that. I

The article also links to Haxe. It looks like Haxe does not come with a cross-platform UI framework, but there are some projects that appear to do just that. It seem that indeed Flow9 is the only thing I'm aware of that provides a great cross platform UI framework. There is Qt which targets desktop and mobile, and there are a whole bunch of JS solutions that target some but not all platforms. I'm a bit weary of learning the language on its own merits, as it does not really seem to innovate over what I already know, but if I'd had to write a cross-platform app, it's definitely worth considering.