PurgeCSS : PurgeCSS is a tool to remove unused CSS. It can be part of your development workflow.
stylelint : A mighty, modern CSS linter that helps you enforce consistent conventions and avoid errors in your stylesheets.
Galen Framework : Automated testing of look and feel for your responsive websites.
Layout testing seemed always a complex task. Galen Framework offers a simple solution...
Sizzy : A tool for developing responsive websites crazy-fast.
Open sourced : https://github.com/kitze/sizzy
csscss : csscss will parse any CSS files you give it and let you know which rulesets have duplicated declarations.
UnCSS is a tool that removes unused CSS from your stylesheets. It works across multiple files and supports Javascript-injected CSS.