List of awesome CSS frameworks.
Feel free to contribute.

Are you looking for React/Vue/Angular UI Component Libraries instead?

• Base / Reset / Normalize
• Class-less
• Very Lightweight
• General Purpose
• Material Design
• Utility-based
• Specialized
• Stalled Development

• modern-normalize - Normalize browsers' default style.
  Repo | #CSS

• ress - Modern CSS reset.
  Repo | #CSS

• Natural Selection - Collection of best-practice CSS selectors.
  | #CSS

Frameworks that use semantic HTML and do not rely on classes.

• Pico.css - Elegant styles for all native HTML elements, dark mode automatically enabled.
  Demo, Docs, Repo | #SCSS

• MVP.css - Minimalist stylesheet for HTML elements.
  Docs, Repo | #CSS

• sakura - Minimal classless CSS framework/theme.
  Demo, Repo | #SCSS

• Simple.css - Lightweight, classless CSS framework.
  Demo, Docs, Repo | #CSS

• Tacit - CSS framework for dummies, without classes.
  Repo | #SCSS

Frameworks that are smaller than ~10KB.

• Pure - Set of small, responsive CSS modules that you can use in every web project.
  Demo, Docs, Repo | #CSS

• Picnic CSS - Lightweight and beautiful library.
  Demo, Docs, Repo | #SCSS

• Chota - Really small CSS framework.
  Demo, Docs, Repo | #CSS

• Bootstrap - The most popular HTML, CSS, and JavaScript framework for developing responsive, mobile first projects on the web.
  Demo, Docs, Repo | #SCSS

• Bulma - Modern CSS framework based on Flexbox.
  Demo, Docs, Repo | #Sass

• Foundation - The most advanced responsive front-end framework in the world.
  Demo, Docs, Repo | #SCSS

• UIkit - Lightweight and modular front-end framework for developing fast and powerful web interfaces.
  Demo, Docs, Repo | #LESS #SCSS

• Primer - CSS framework that powers GitHub's front-end design.
  Docs, Repo | #SCSS

• Carbon Components - Component library behind IBM's Carbon Design System.
  Docs, Repo | #SCSS

• U.S. Web Design System - Components used by U.S. federal government websites.