Recently, my wife has been learning to program JavaScript using Codecademy. I like how it walks people through exercises step by step, and builds up concepts, etc. All the marking is automated, and there are hints available so you never get stuck. It allows multiple different answers which have equivalent meaning (so, it's not as simple as just fill in the blank).
I'd like to find something equivalent for learning/practicing written Chinese. Does such a thing exist? If so, where can I find it?
(I'm also hoping for characters [Simplified], rather than Pinyin).