Bootstrap - Simple and flexible HTML, CSS, and JS for popular UI components and interactions
Tailwind CSS - A utility-first CSS framework for rapidly building custom user interfaces.
Elastic UI - React-based design library made for use with Elastic products
Materialize CSS - A modern responsive front-end framework based on Material Design
Semantic UI - A UI Component library implemented using a set of specifications designed around natural language
UIKit - A lightweight and modular front-end framework for developing fast and powerful web interfaces