CoffeeScript - Little language that compiles into JavaScript

CoffeeScript is a little language that compiles into JavaScript. It's just JavaScript, the code compiles one-to-one into the equivalent JS, and there is no interpretation at runtime. You can use any existing JavaScript library seamlessly from CoffeeScript (and vice-versa). The compiled output is readable and pretty-printed, will work in every JavaScript runtime, and tends to run as fast or faster than the equivalent handwritten JavaScript.