Grunt

http://gruntjs.com

is a Javascript Task Runner which can perform repetitive tasks for you like minification, compilation, unit testing, linting etc.

Grunt has hundreds of plugins that help you to automate the tasks.

Nice quick video

https://www.youtube.com/watch?v=q3Sqljpr-Vc

JsHint: JSHint is a program that flags suspicious usage in programs written in JavaScript. The core project consists of a library itself as well as a CLI program distributed as a Node module.

CoffeeScript is a little language that compiles into JavaScript. Underneath that awkward Java-esque patina, JavaScript has always had a gorgeous heart. CoffeeScript is an attempt to expose the good parts of JavaScript in a simple way.

RequireJS is a JavaScript file and module loader. It is optimized for in-browser use, but it can be used in other JavaScript environments, like Rhino and Node. Using a modular script loader like RequireJS will improve the speed and quality of your code.

Stylus: