Bootstrap - Simple and flexible HTML, CSS, and JS for popular UI components and interactions
Purecss - A set of small, responsive CSS modules that you can use in every web project.
Materialize CSS - A modern responsive front-end framework based on Material Design
Vuetify - Material Component Framework for VueJS 2
HTML5 Boilerplate - A rock-solid default for HTML5 awesome.
Foundation - The most advanced responsive front-end framework in the world