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.
Sprite Cow : Sprite Cow helps you get the background-position, width and height of sprites within a spritesheet as a nice bit of copyable css.
* { CSS:resetr } : To help you find the perfect CSS-reset styles, CSSresetr lets you try all the best CSS Resets on a variety of web pages – even your own.
enquire.js : A lightweight, pure JavaScript library for responding to CSS media queries.