This is quite impressive technically, and I think the type-checking feature alone can make it appeal to those making large-scale application in collaborative development environment. I hope this inspires other similar efforts. A quick run-down of features:

- It's a superset of JavaScript. So there is no porting effort needed. (With CoffeeScript, you do not need to port if you don't want to.)

- compile-time type checking, like type erasure in Java's generics.

- module support at the language level. It's very thin. It does not give your AMD or CommonJS module, but you can easily hack around it.

- class and inheritance support at the language level. The implementation is very similar to CoffeeScript's.