Vaultwarden is a self-hosted, open-source password manager server that provides a full Bitwarden-compatible API. Written in Rust using the Rocket web framework, it implements the entire Bitwarden client API for vault management, organizations, SSO/OIDC authentication, two-factor authentication (TOTP, WebAuthn, Duo, YubiKey, email), secure file storage, send functionality, emergency access, event logging, and push notifications. The architecture is a monolithic web service backed by Diesel ORM supporting SQLite, MySQL, PostgreSQL, and CockroachDB. File attachments are stored via an OpenDAL abstraction (local filesystem or S3). The server is deployed as a single binary or Docker container, serving its own web vault UI and an admin panel. External dependencies include the Bitwarden push relay service for mobile notifications and the upstream Bitwarden protocol for client compatibility. The codebase is well-structured with clear separation of concerns, extensive migrations, and a comprehensive Playwright test suite. It is actively maintained and widely adopted with over 68k stars.