Radix UI is an open-source collection of tools for building web interfaces, mainly with React. It is designed to help developers create accessible and customizable user interfaces without starting from scratch.

The product includes:

Radix Primitives: unstyled, accessible React components such as dialogs, dropdowns, popovers, tooltips, and tabs.
Radix Themes: a styled component library built on the primitives.
Radix Colors: accessible color scales for interface design.
Radix Icons: a set of crisp, ready-to-use icons.

Because the primitives are unstyled, they can be used with many CSS and styling solutions. They work in React web applications, including frameworks such as Next.js, Remix, Vite, Gatsby, and Create React App, and support both client-side and server-side rendering.

Radix UI is useful for developers and design system teams that want accessible building blocks, flexible styling, and reusable components for modern web applications.