A friend and I just started Layx: a new layout language based on Cassowary, the constraint solving toolkit that Apple is using for their user interfaces. It's only for web now, but it will be multiplatform -mobile natively- someday.
It is designed to be extremely simple and easy (like python), and as asked, it compiles internally to HTML, dynamically, as the interface has to be updated if layers have to be moved or resized.
It's a really new project -alpha version-, so try it knowing that.
Project website: http://www.layx.org/
Online demo: http://www.layx.org/demo/
Open Source repository: http://github.com/layxlang/layx
I hope it helps and feedback is always welcome!
Regards
EDIT (8 Jan, 2015): Open source link added
EDIT (15 Jan, 2015): Demo link added
