HeroUI (formerly NextUI) is a production-grade React UI component library built on React Aria Components (RAC) and Tailwind CSS v4. It provides a comprehensive set of accessible, compound components (e.g., Button, Select, Calendar, Modal, Table) with a type-safe variant system powered by tailwind-variants. The library emphasizes accessibility (WAI-ARIA), SSR compatibility, and deep customizability via render props, BEM slot classes, and data-slot attributes. The monorepo includes a Next.js documentation site with bilingual (en/cn) interactive demos, a theme builder for live design token customization, Storybook for visual development, and AI-native features such as an MCP server, llms.txt endpoints, and an embedded Docs Agent for AI-assisted documentation queries. The codebase demonstrates strong engineering practices: compound component pattern, context-based slot propagation, reusable hooks (useOverlayState, useMeasuredHeight), and a dual testing strategy (SSR smoke tests + browser interaction tests). While the library is well-maintained and actively developed, its tight coupling to react-aria-components and the large demo surface (duplicated across languages) present moderate maintenance risks.