Gridlex - Simple. Robust. Responsive. Flexible.
Bootstrap - Simple and flexible HTML, CSS, and JS for popular UI components and interactions
Unsemantic CSS Framework - Unsemantic is a fluid grid system that is the successor to the 960 Grid System.
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.
960 Grid System - The 960 Grid System is an effort to streamline web development workflow by providing commonly used...
react-md - Google's Material Design UI Components built with accessibility in mind, Sass, And React.