Sass vs. Less vs. Bourbon

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.

Bourbon is a library of pure sass mixins that are designed to be simple and easy to use. No configuration required. The mixins aim to be as vanilla as possible, meaning they should be as close to the original CSS syntax as possible.