Diffgram is a full-stack data annotation platform designed for creating, managing, and reviewing annotations on images, video, audio, text, 3D point clouds, and geospatial data. The system is composed of multiple microservices: a Flask-based REST API (`default`), a background processing service (`walrus`) for media ingestion, export generation, and project migration, an event-driven action runner service (`eventhandlers`) that executes automated workflows (e.g., ML model inference, webhooks, exports), and a Vue 2 + Vuetify single-page application frontend. The backend uses PostgreSQL with SQLAlchemy ORM, RabbitMQ for async messaging, and supports multiple cloud storage backends (AWS S3, GCP, Azure, MinIO). Authentication supports OAuth2/Keycloak, API keys, and session cookies with fine-grained role-based permissions. The platform's core domain includes label schemas, attribute groups, instance templates, task/job management with review workflows, discussions/issues, and a custom query engine for filtering files by labels and attributes. It integrates with external AI services (HuggingFace, Vertex AI, Azure Text Analytics) and labeling vendors (Labelbox, Scale AI). The frontend provides rich annotation tools including 2D canvas (boxes, polygons, keypoints), 3D point cloud annotation with Three.js, audio waveform annotation, text token annotation, and geospatial tile annotation. A command pattern enables undo/redo for annotation actions. The codebase demonstrates solid engineering practices with clear separation of concerns, reusable patterns (strategy, observer, command, policy enforcer), and extensive test coverage (Cypress E2E, Jest unit tests, Python unittest). However, there are signs of technical drift: some outdated dependencies, mixed JavaScript/TypeScript in the frontend, and a few legacy modules marked as deprecated. The open-core model is evident from `OPENCORE - ADD` markers, suggesting proprietary extensions. Overall, Diffgram is a mature, actively maintained annotation platform suitable for teams building training data pipelines.