Atlas is a database schema management tool that supports both declarative and versioned workflows. It provides a CLI interface for inspecting, diffing, and applying schema changes across multiple databases (MySQL, PostgreSQL, SQLite, SQL Server, CockroachDB, etc.). The architecture is modular, with core packages for database drivers (sqlclient), migration planning/execution (migrate), HCL-based schema definition (schemahcl), and safety checking (sqlcheck). Key entry points are in cmd/atlas/internal/cmdapi for schema, migrate, and version commands. The system uses Ent ORM for migration state tracking and includes advanced features like drift detection, cloud integration, and a scripting engine for conditional migrations.