stylecow’s main purpose is to bring more CSS support to all browsers. Stylecow converts your code to be more compatible with all browsers adding vendor prefixes, fixing issues, generating polyfills, etc.
You can play also with latests (or futures) css features such variables, nested rules or color manipulation using the w3c syntax. This mean you don’t have to learn another language such LESS or SASS to use variables or color manipulation, you write css and you get css, and if you stop using stylecow, your css code remains css code.
To get started, go to its project website