This is really cool, and I've wanted something like this to hack on for ages. I'm a big fan of being able to present concepts along with code that you can run, and I'm also a huge fan of not having to rely on a server backend. I have a static blog where I try to talk about various math concepts which I illustrate with code. I hacked together a pseudo-literate html sort of presentation, and it works just fine, but it's inflexible.