varlet is an open-source Vue project in the testing space with 5.3k GitHub stars. The repository is actively maintained, with recent commits.

zag is an open-source TypeScript project in the ui components space with 5.1k GitHub stars. The repository is actively maintained, with recent commits.

Composio is an integration platform that gives AI agents and LLMs authenticated access to hundreds of external tools and apps (Gmail, Slack, GitHub, etc.) through a managed SDK, handling OAuth, auth config, and tool execution so agents can take real-world actions.

A Microsoft-maintained library of Razor/Blazor UI components implementing the Fluent Design System, giving .NET 8/9 web apps the look and feel of modern Microsoft applications. It wraps Fluent UI Web Components and adds Blazor-native components like DataGrid, dialogs, toasts, and design-token customization.

Fusion Next (@alifd/next) is Alibaba's enterprise-class React UI component library built around a design-system collaboration workflow, letting designers customize component themes and ship them as npm packages that developers consume without manual UI rework.

radzen-blazor is an open-source C# project in the ui components space with 4.3k GitHub stars. The repository is actively maintained, with recent commits.

basecoat is an open-source JavaScript project in the ui components space with 4k GitHub stars. The repository is actively maintained, with recent commits.

Tailwind CSS is a utility-first CSS framework that lets you build custom designs directly in your markup by composing low-level utility classes instead of writing custom CSS. It generates only the styles you use via a build step, keeping output small.

Bulma is a free, open-source CSS framework based on Flexbox that provides ready-to-use, responsive UI components and a grid system without requiring any JavaScript. It's distributed as a single CSS file or as customizable Sass source.

Materialize is a responsive front-end CSS/JS framework that implements Google's Material Design language, providing styled HTML components, layout grids, and interactive JavaScript widgets out of the box.

PostCSS is a tool for transforming CSS with JavaScript plugins. It parses CSS into an abstract syntax tree, lets plugins inspect and mutate it, then stringifies the result — powering everything from autoprefixing to future-syntax polyfills and minification.

Pico is a minimalist, lightweight CSS framework that styles semantic HTML elements beautifully out of the box, requiring few or no classes. It offers a class-less mode, dark/light themes, SASS customization, and a small set of components, acting like a supercharged CSS reset.

Omi is a lightweight web components framework from Tencent that combines Custom Elements, JSX/function components, and signal-driven reactivity. It supports both OOP class components and data-oriented reactive functions, and produces standards-based components usable across React, Vue, and plain HTML.

Primer CSS is the SCSS/Sass implementation of GitHub's Primer Design System, providing utility classes and component styles distributed via npm. It's now in maintenance ("KTLO") mode, with GitHub steering new work toward primer/react and primer/view_components.

Spectre.css is a lightweight (~10KB gzipped) CSS framework built around a Flexbox-based responsive grid, base styles, and a set of pre-styled components and utilities. It's a Sass-customizable starting point for building modern, mobile-friendly UIs without JavaScript.

cdnjs is a free, open-source content delivery network that hosts the static assets (JS, CSS, fonts, etc.) of thousands of popular web libraries, letting developers include them via a public CDN URL. This particular repository is the robot-only asset store; library metadata and contributions live in separate repos.

Milligram is an ultra-lightweight (~2kb gzipped) CSS framework that provides minimal default styling for typography, forms, buttons, grids, and tables. It aims to be a clean, low-opinion starting point rather than a full UI component library.

A UI kit that layers Google's Material Design styling on top of Bootstrap 4, providing a large library of pre-built components, animations, icons, and templates. This jQuery-based version is the legacy v4 release, with the project now steering users toward a Bootstrap 5 successor.

metroui is an open-source JavaScript project in the ui components space with 7.1k GitHub stars. The repository has seen commits within the last year.

Charts.css is a dependency-free CSS framework for data visualization that turns semantic HTML tables into charts and graphs using utility classes and CSS variables. Instead of JavaScript or SVG/canvas rendering, it styles markup directly so charts are accessible, lightweight, and customizable with plain CSS.