Milligram : Milligram provides a minimal setup of styles for a fast and clean starting point. Just it! Only 2kb gzipped! It's not about a UI framework. Specially ...
Symfony : Symfony is a set of reusable PHP components and a PHP framework for web projects.
Pure : A set of small, responsive CSS modules that you can use in every web project.
xCSS bases on CSS and empowers a straightforward and object-oriented workflow when developing complex style cascades.