CoffeeScript does look a bit like HAML. But actually, to write CoffeeScript, you write CoffeeScript, not HAML, and then you can either compile it with the coffee command (which does output JS) and run the JS on the server OR on the client (see http://jashkenas.github.com/coffee-script/#scripts). Actually more often its on the server because people don't like running it in the browser (I don't see a good reason to avoid CoffeeScript in the browser really, but he says its "not recommended" on his site so.. people don't feel its recommended.)