Open source. Open possibilities.

Franken UI (franken-ui/ui) is described as an HTML-first UI component library built on UIkit 3, extended with LitElement and inspired by shadcn/ui. Its README now only announces a move to 0build, so documentation lives elsewhere.

Braid is SEEK Group's themeable design system, distributed as a React component library. It provides themes, BraidProvider, and components styled with Vanilla Extract, with setup guidance for sku-based projects.

Bulma is a modern, Flexbox-based CSS framework distributed as a single CSS file with no JavaScript. It offers Sass sources for variable customization and works with any frontend stack.

Numl is a deprecated UI design language, web-component library and runtime CSS framework for quickly building interfaces that follow a design system, loadable with a single JavaScript module and no bundler or config.

OpenCosmos is an open-source creative platform and design system ecosystem built on human-centered principles. It includes a portfolio site, community platform, AI-powered investment app, and a personal OS concept, all unified by the OpenCosmos/UI component library.

Priceline Design System is Priceline.com's open-source UI component library and design standard. It aims to unify interface patterns, speed design and development, and promote accessibility, internationalization, and responsive web design. It ships as the npm package pcln-design-system with Storybook docs and an MIT license.

Spruce CSS is an open-source, lightweight Sass-based CSS design system and framework offering variables, mixins, functions, few utility classes and CSS custom property theming with dark mode.

oh-my-design installs design system references and skills into AI coding agents. One command adds 440+ company design references, 28 skills, and 20 specialist roles to Claude Code, Codex, Cursor, and OpenCode. Produces a portable DESIGN.md with philosophy, tokens, and component contracts.

Chromatic is a build tool for managing cross-platform design systems from design-token files. It supports expressive token expressions, themes, YAML/JSON input, and generates Sass, CSS, iOS, Android, and HTML style-guide outputs.

A Svelte 5 UI component library inspired by Vercel's Geist, aimed at helping developers build cohesive and consistent web experiences. It ships with an online documentation site and is released under the MIT license.

A lightweight, modular and customizable design system built with vanilla CSS, using CSS variables, mobile-first responsive principles and accessibility practices. It includes examples, design tokens, build and lint scripts, format conversion, and a CDN-ready combined CSS file.

Catppuccin is a community-driven pastel color theme offering four warm flavors with 26 colors each, plus documentation, style guide, and cross-tool integrations.

Helsinki Design System (HDS) is an open-source design system from the City of Helsinki, offering accessible React components, CSS styles and design tokens, alongside documentation and design resources.

HeroUI, formerly NextUI, is a production-ready React component library combining React Aria accessibility with Tailwind CSS v4. It offers compound components, per-component packages, and AI-oriented tooling such as an MCP server, llms.txt, and agent skills.

GitHub Dark is a userstyle project that applies a dark theme to GitHub, reducing eye strain during coding sessions. It includes syntax highlighting themes for GitHub, CodeMirror, and Jupyter, and is designed to be used with browser extensions like Stylus.

DesignMD is a CLI tool that extracts live design systems from any URL — colors, typography, spacing, breakpoints, and interaction states — and outputs a portable DESIGN.md file optimized for AI coding agents.

Material Design for Bootstrap is a free UI kit offering 700+ components, themes, and templates for building responsive, mobile-first websites. Available for jQuery, Angular, React, and Vue under MIT license.

Vant is a lightweight, customizable Vue UI component library for mobile web apps, offering 80+ components with zero third-party dependencies, TypeScript support, and compatibility with Vue 2/3, Nuxt, SSR, dark mode and i18n.

An imperative Swift 6 wrapper for GTK4 and libadwaita, offering 178 type-safe widget wrappers, fluent setters, async/await, and full GNOME desktop app support on Linux and macOS.

CompoMo (@ds-mo/ui) is a framework-agnostic Stencil.js web component library styled with TokoMo design tokens, shipping generated Angular, React and Vue adapters alongside an MCP metadata server.