Sizzy : A tool for developing responsive websites crazy-fast.
Open sourced : https://github.com/kitze/sizzy
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.
Compass : Compass is an open-source CSS Authoring Framework.
📦 Parcel : Blazing fast, zero configuration web application bundler
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...
csscss will parse any CSS files you give it and let you know which rulesets have duplicated declarations.