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...
UnCSS : UnCSS is a tool that removes unused CSS from your stylesheets. It works across multiple files and supports Javascript-injected CSS.
BackstopJS : Breaking CSS is easy. Checking every responsive page element is hard. That’s why there's BackstopJS.
stylelint : A mighty, modern CSS linter that helps you enforce consistent conventions and avoid errors in your stylesheets.
Skeleton : Skeleton: A Dead Simple, Responsive CSS Boilerplate for Mobile-Friendly Development