Spectre.css : Spectre.css is a lightweight, responsive and modern CSS framework for faster and extensible development.
lightweight and clean starting point for your...
UIkit : A lightweight and modular front-end framework
for developing fast and powerful web interfaces.
xCSS : xCSS bases on CSS and empowers a straightforward and object-oriented workflow when developing complex style cascades.
A utility-first CSS framework packed with classes like flex, pt-4, text-center and rotate-90 that can be composed to build any design, directly in your markup.