Basically, it allows you to style your native iOS app with CSS like a website instead of using Apples native styling. For example I have this game and I can make a css file to create and/or change the color scheme of my app. Here is an example of some themes all generated from LESS css files[1].
http://www.pixate.com/docs/framework/ios/2.0/style-reference...
Similar to NUI https://github.com/tombenner/nui
I'm using it. Easier than UIAppearance, but still need some improvements in handling UICollection (it lags). However, overall is good.