Mockoon is a multi-platform API mocking tool that runs mock servers locally or remotely. It is built as a monorepo with six npm packages: @mockoon/commons (shared models, migrations, OpenAPI converter), @mockoon/commons-server (core Express-based mock server engine with templating and response rules), @mockoon/app (Electron desktop application with an Angular renderer), @mockoon/cli (oclif-based command-line interface), @mockoon/cloud (cloud sync library), and the deprecated @mockoon/serverless wrapper. The architecture cleanly separates the core server logic from the delivery mechanisms. The MockoonServer class provides an HTTP/HTTPS server with a sophisticated response rule engine, a Handlebars templating system with over 100 custom helpers (including deep Faker.js integration), CRUD operations on data buckets, WebSocket support, proxy mode, and a full admin API. The desktop app uses a Redux-like state management pattern with RxJS, ensuring predictable and testable UI state transitions. The codebase demonstrates high craftsmanship in several areas. The ResponseRulesInterpreter is a self-contained DSL for matching HTTP requests to mock responses. The TemplateParser provides an extensible helper registration system. The data migration system in commons is a textbook example of handling schema evolution for JSON-based data models. The project is actively maintained with a robust CI/CD pipeline, though it carries some technical debt such as a deprecated serverless package and disabled strict TypeScript mode in the desktop app.