Here is a list of frameworks, that either have full CSS + JS suite of modules (or blocks) or are just CSS-only.

Type Name URL Notes
Full Bootstrap http://getbootstrap.com/ most popular
Full Material UI http://www.material-ui.com/ second most popular
Full Zurb Foundation https://foundation.zurb.com/sites/getting-started.html
Full Semantic-UI https://semantic-ui.com/introduction/getting-started.html
Full Clarity UI https://vmware.github.io/clarity/get-started
Full Metro UI https://metroui.org.ua
Full UIkit https://getuikit.com/docs/introduction
CSS Bulma https://bulma.io
CSS Tachyons http://tachyons.io/
CSS Pure.css https://purecss.io
CSS Spectre https://picturepan2.github.io/spectre/
CSS Skeleton http://getskeleton.com
CSS Tailwind https://tailwindcss.com/docs/what-is-tailwind/ WIP
CSS Sakura https://oxal.org/projects/sakura/ very minimal
CSS Base http://getbase.org extremely minimal

Web Components:

Name URL
Polymer https://www.polymer-project.org

Web App frameworks:

Name URL
Vue.js https://vuejs.org/v2/guide/
React https://reactjs.org
Angular https://angular.io/guide/quickstart