TriliumNext/Trilium is a full-stack, cross-platform hierarchical note-taking application with rich text editing, LLM integration, sync, encryption, and a plugin-based architecture. The monorepo contains a Node.js Express server (SQLite backend), a Preact/React SPA client, an Electron desktop wrapper, a standalone browser-SQLite-WASM build, and a Capacitor mobile app. The system manages notes as a tree with cloning, attributes, relations, and multiple content types (text, code, mind maps, canvases, spreadsheets, calendars, etc.). It provides custom CKEditor5 plugins for math, footnotes, mermaid diagrams, and AI assistance, as well as a full-featured LLM chat with tool execution and skill sheets. The codebase is well-tested with over 2000 spec files, uses modern TypeScript and pnpm workspaces, and includes comprehensive import/export (Evernote, OneNote, Obsidian, Notion, Google Keep, OPML, Markdown, HTML) and sync capabilities. Key architectural patterns include a provider abstraction for platform-specific services (crypto, zip, messaging, clipboard), a component-based widget system on the client, and a centralized entity cache (becca/froca) that is synchronized via WebSocket.