7.css: A tiny CSS framework for building faithful recreations of the Windows 7 UI.

98.css: A design system for building faithful recreations of old UIs.

AESTHETIC CSS: A vaporwave CSS framework. 🌴🐬

Amaze UI: A mobile-first and modular front-end framework.

animate.css: A cross-browser library of CSS animations. As easy to use as an easy thing.

Avalanche: A package based CSS framework.

aqua.css: A elegant CSS Framework.

awsm.css: Simple CSS library for semantic HTML markup.

Bahunya: 10KB classless CSS framework with responsive typography, navbar, syntax highlighting, etc.

base: A Rock Solid, Responsive CSS Framework built to work on all devices big, small and in-between.

Basic.css: Classless CSS Starter File.

basscss: Low-level CSS Toolkit – the original Functional/Utility/Atomic CSS library.

Beercss: Build material design interfaces in record time... without stress for devs... 🍺💛

Blitz: An eBook Framework (CSS + template).

Bojler: Is a CSS framework for email's.

bonsai.css: A Utility Complete CSS Framework for less than 45kb (8kB Gzipped).

Bootflat: Is an open source Flat UI KIT based on Bootstrap 3.3.0 CSS framework. It provides a faster, easier and less repetitive way for web developers to create elegant web apps.

BOOTSTRA.386: A vintage 1980s DOS inspired Twitter Bootstrap theme.

bootstrap: The most popular HTML, CSS, and JavaScript framework for developing responsive, mobile first projects on the web.

bourbon: A Lightweight Sass Tool Set.

bulma: Modern CSS framework based on Flexbox.

Caramel.CSS: A simple to use, easy to remember css framework.

carbon: A design system built by IBM.

Centurion: Is a web-based framework for rapid prototyping and building larger web projects.

Charts.css: Open source CSS framework for data visualization.

chota: A micro (3kb) CSS framework.

Cirrus: The SCSS framework for the modern web.

classic.css: Generate a Classic Mac interface in your browser.

codyhouse-framework: A lightweight front-end framework for building accessible, bespoke interfaces.

Concise.css: A CSS framework that's lightweight and easy-to-use. Give up the bloat. Stop tripping over your classes. Be Concise.

css-buttons: 100 Modern CSS Buttons, Free And Royalty Free.

cssfx: ✨ Beautifully simple click-to-copy CSS effects.

cutestrap: A strong, independent CSS Framework. Only 2.7KB minified & gzipped.

daisyui: The most popular, free and open-source Tailwind CSS component library.

Element: A Vue 2.0 based component library for developers, designers and product managers.

elementary.css: Elementary OS's stylesheet converted to browser CSS.

Filters.css: CSS only library to apply color filters.

flexboxgrid: Grid based on CSS3 flexbox.

fluidity: The worlds smallest fully-responsive css framework.

Fomantic-UI: Is the official community fork of Semantic-UI.

foundation-sites: 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.

furatto: It's a flat, fast and powerful front-end framework for rapid web development.

geo-bootstrap: A timeless Twitter Bootstrap theme built for the modern web.

Gutenberg: Modern framework to print the web correctly.

hack: ⛷ Dead simple CSS framework.

Halfmoon: Front-end framework with a built-in dark mode and full customizability using CSS variables; great for building dashboards and tools.

hiq: A lightweight, progressive, high-IQ CSS framework.

Homebrewery: A CSS stylesheet to create authentic looking D&D homebrews.

Hover: A collection of CSS3 powered hover effects to be applied to links, buttons, logos, SVG, featured images and so on. Easily apply to your own elements, modify or just use for inspiration. Available in CSS, Sass, and LESS.

inuitcss: Extensible, scalable, Sass-based, OOCSS framework for large and long-lasting UI projects.

IsometricSass: Sass library to make isometric 2D without javascript

Jeet: The most advanced, yet intuitive, grid system available for Sass or Stylus.

knopf.css: Modern, modular, extensible button system designed for both rapid prototyping and production-ready applications.

lit: World's smallest responsive 🔥 css framework (395 bytes).

material-components-web: Modular and customizable Material Design UI components for the web.

Materialize

mdb-ui-kit: Bootstrap 5 & Material Design 2.0 UI KIT.

Metro 4: Impressive component library for expressive web development! Build responsive projects on the web with the first front-end component library in Metro Style. And now there are even more opportunities every day!

milligram: A minimalist CSS framework.

mini.css: A minimal, responsive, style-agnostic CSS framework!

minireset.css: A tiny modern CSS reset.

mobi.css: A lightweight, scalable, mobile-first CSS framework.

modern-css-reset: A bare-bones CSS reset for modern web development.

modern-normalize: 🐒 Normalize browsers' default style.

mui: A lightweight CSS framework that follows Google's Material Design guidelines.

MVP.css: Minimalist stylesheet for HTML elements.

Natural Selection: A CSS Boilerplate / Starter Kit: Collection of best-practice CSS selectors.

NES.css: NES-style CSS Framework | ファミコン風CSSフレームワーク.

normalize.css: A modern alternative to CSS resets.

papercss: The Less Formal CSS Framework.

patternfly: An open source design system built to drive consistency and unify teams.

Phonon: A responsive front-end framework with a focus on simplicity and flexibility.

picnic: A beautiful CSS library to kickstart your projects.

pico: Minimal CSS Framework for semantic HTML.

primer: The CSS design system that powers GitHub.

primitive: ⛏️ ‎ A front-end design toolkit for developing web apps.

Propeller: Develop more, Code less. A front-end responsive framework based on Google's Material Design Standards & Bootstrap.

PSone.css: 🎮 PS1 style CSS Framework, inspired by NES.css

Puppertino: A CSS framework based on Human Guidelines from apple.

pure: A set of small, responsive CSS modules that you can use in every web project.

Ratchet: Build mobile apps with simple HTML, CSS, and JavaScript components.

Responsive: A super lightweight HTML, Sass, CSS, and JavaScript framework for building responsive websites.

ress: 🚿 A modern CSS reset.

RPGUI: Lightweight framework for old-school RPG GUI in web!.

sakura: A minimal css framework/theme.

sanitize.css: A best-practices CSS foundation.

Semantic-UI: a UI component framework based around useful principles from natural language.

simple.css: Is a classless CSS template that allows you to make a good looking website really quickly.

siimple: The minimal and themeable CSS toolkit for flat and clean designs.

Skeleton: A Dead Simple, Responsive Boilerplate for Mobile-Friendly Development.

Skin: Pure CSS framework designed & developed by eBay for a branded, e-commerce marketplace. Created by eBay.

slim.js: Fast & Robust Front-End Micro-framework based on modern standards.

SPCSS: A simple, minimal, classless stylesheet for simple HTML pages.

spectre: A Lightweight, Responsive and Modern CSS Framework.

susy: Responsive layout toolkit for Sass.

Tabler: Free and open-source HTML Dashboard UI Kit built on Bootstrap.

tacit: CSS framework for dummies, without a single CSS class.

tailwindcss: A utility-first CSS framework for rapid UI development.

tawian-frontend: A markdowny CSS framework.

tentcss: A CSS survival kit. Includes only the essentials to make camp.

terminal.css: Modern and minimalistic CSS framework for terminal enthusiasts.

TuiCss: A text-based user interface CSS library.

turretcss: A framework for rapid development of responsive and accessible websites.

uikit: A lightweight and modular front-end framework for developing fast and powerful web interfaces.

universal.css: The only CSS you will ever need.

unnamed-css-framework: A simple colorful CSS framework.

unsemantic: Fluid grid for mobile, tablet, and desktop.

Vanilla: A simple, extensible CSS framework.

Vital: A minimally invasive CSS framework for modern web applications.

water.css: A drop-in collection of CSS styles to make simple websites just a little nicer.

wing: A beautiful CSS framework designed for minimalists.

wired-elements: A collection of custom elements that appear hand drawn. Great for wireframes or a fun look.

Wireframe: A minimal wireframing css-framework. 🎈

XP.css: A CSS framework for building faithful recreations of operating system GUIs.