stylelint : A mighty, modern CSS linter that helps you enforce consistent conventions and avoid errors in your stylesheets.
csscss : csscss will parse any CSS files you give it and let you know which rulesets have duplicated declarations.
Ink : Ink provides the same component-based UI building experience that React offers in the browser, but for command-line apps. It uses Yoga to build Flexbo...
Phantomas : PhantomJS-based web performance metrics collector and monitoring tool
Sizzy : A tool for developing responsive websites crazy-fast.
Open sourced : https://github.com/kitze/sizzy
PurgeCSS is a tool to remove unused CSS. It can be part of your development workflow.