http://livecode.com/
This looks like a compelling solution for cross-platform development. The scripting language is a bit verbose but it looks capable. I've skimmed the user guide and it's fairly extensive. I feel like I could whip something up pretty quickly. I'm hoping to play around with LiveCode if ever get some spare time.
I'm curious about other people's experiences with LiveCode. I'm mostly interested in whether there was a productivity gain over something like Haxe/OpenFL, C++/Qt, or Python/Kivy. I'd like to target desktop and mobile and LiveCode appears to be a good choice.