Mastodon is a full-stack, federated social network server implementing the ActivityPub protocol. It provides a production-grade Rails API backend with a React/Redux frontend, real-time streaming via Node.js, and extensive background job processing with Sidekiq. The system supports user timelines, media attachments, content moderation, admin dashboards, OAuth authentication, and federation with other ActivityPub-compatible services. The codebase is large and actively maintained, with a clear separation of concerns across controllers, services, serializers, workers, and frontend components. It includes advanced features such as trending content, annual user reports, FASP data sharing, and a comprehensive admin interface. While the architecture is well-structured, there are signs of technical drift including mixed frontend patterns (legacy JSX vs modern TypeScript/Redux Toolkit), placeholder Ruby/Node version numbers, and some deprecated API endpoints.