HTML/CSS/JavaScript

Get something in front of users. The web is the easiest way. It's better than cross platform, it's hardware independent. There's no approval process. AB testing and iteration are low friction for a developer. There's no one sitting between you and your first ten users. You can offer demos without signup or installation or sending codes.

Besides, every app needs a web page anyway. Native look and feel is a feature not a function.

Good luck.

You might want to write the common elements in C or C++ (or whatever language you like that can be compiled into a static library), then write separate glue code for each platform. This is one tutorial that describes the technique: http://www.skyscanner.net/blogs/developing-mobile-cross-plat...

Looks pretty interesting. If I'm reading it correctly I'd still need to build two UIs? That's kind of what I was looking to avoid -- I'm assuming it's difficult. But the WebView based solutions I've seen always look kind of janky.

Cordova