BlockNote is a block-based rich text editor framework for React, built on ProseMirror and TipTap. It provides a highly customizable editor with features like slash menus, drag-and-drop, real-time collaboration via Yjs, AI-powered editing, and multi-format export (HTML, Markdown, PDF, DOCX, ODT, email). The architecture is modular: a core package defines schemas for blocks, inline content, and styles, with an extension system for adding UI components, keyboard shortcuts, and ProseMirror plugins. Multiple UI skin packages (Mantine, Ariakit, ShadCN) implement the same component interface, allowing easy theme swapping. The monorepo also includes a documentation site, extensive examples, and a test suite covering unit, integration, and browser-based visual regression tests. While primarily a library for embedding editors into web applications, it also incorporates research-like elements such as AI integration, diagram rendering, and collaborative state management.