Bulma - Bulma is an open source CSS framework based on Flexbox and built with Sass. It's 100% responsive, fully modular, and available for free.
WING - A phone carrier that is actually nice to you.
Spectre.css - Lightweight, responsive and modern CSS framework for faster and extensible development.
Puppertino - A CSS framework based on Apple's design and human guidelines
Material UI - A CSS Framework and a Set of React Components that Implement Google's Material Design
Tailwind CSS - A utility-first CSS framework for rapidly building custom user interfaces.