UnCSS : UnCSS is a tool that removes unused CSS from your stylesheets. It works across multiple files and supports Javascript-injected CSS.
CSS Lint : CSS Lint points out problems with your CSS code. It does basic syntax checking as well as applying a set of rules to the code that look for problemati...
csscss : csscss will parse any CSS files you give it and let you know which rulesets have duplicated declarations.
PostCSS plugin to parse CSS and add vendor prefixes to CSS rules using values from Can I Use.