Material UI - A CSS Framework and a Set of React Components that Implement Google's Material Design
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
Polymer - Polymer is a library that uses the latest web technologies to let you create custom HTML elements.
Elastic UI - React-based design library made for use with Elastic products
HTML5 Boilerplate - A rock-solid default for HTML5 awesome.