Materialize CSS - A modern responsive front-end framework based on Material Design
Bootstrap - Simple and flexible HTML, CSS, and JS for popular UI components and interactions
Foundation - The most advanced responsive front-end framework in the world
Purecss - A set of small, responsive CSS modules that you can use in every web project.
Semantic UI - A UI Component library implemented using a set of specifications designed around natural language
HTML5 Boilerplate - A rock-solid default for HTML5 awesome.