Stylus is a revolutionary new language, providing an efficient, dynamic, and expressive way to generate CSS. Supporting both an indented syntax and regular CSS style.
Sass is an extension of CSS3, adding nested rules, variables, mixins, selector inheritance, and more. It's translated to well-formatted, standard CSS using the command line tool or a web-framework plugin.
Less is a CSS pre-processor, meaning that it extends the CSS language, adding features that allow variables, mixins, functions and many other techniques that allow you to make CSS that is more maintainable, themable and extendable.
It is a library that provides binding for Node.js to LibSass, the C version of the popular stylesheet preprocessor, Sass.
It allows you to natively compile .scss files to css at incredible speed and automatically via a connect middleware.