Bootstrap - The most popular HTML, CSS, and JavaScript framework for developing responsive, mobile first projects on the web.
Foundation — The most advanced responsive front-end framework in the world. Quickly create prototypes and production code for sites that work on any kind of device.
Pure — A set of small, responsive CSS modules that you can use in every web project.
Tachyons — Functional css for humans. Quickly build and design new UI without writing css.
PostCSS — Transforming styles with JS plugins. These plugins can lint your CSS, support variables and mixins, transpile future CSS syntax, inline images, and more.
Animate.css — Animate.css is a bunch of cool, fun, and cross-browser animations for you to use in your projects. Great for emphasis, home pages, sliders, and general just-add-water-awesomeness.
Material Design icons — Material design icons are the official icon set from Google that are designed under the material design guidelines.
Bulma — Bulma is a modern CSS framework based on Flexbox.
Hack.css — ⛷️ Dead simple CSS framework. Hack.css is perfect for the homepage of your open-source projects!
CSS Icon — Icon set made with Pure CSS Code. No Dependencies. "Grab and Go" Icons.
bttn.css — Awesome buttons for awesome projects!
aprilFools.css — Harmlessly goof up your co-workers browser and chrome dev tools.