Citadel

Citadel is an open source groupware and messaging platform that combines email and collaboration services in a single server. It uses a room-based architecture to organize discussions and shared content, and can be accessed via web, desktop/mobile clients, and standard protocols.

Key Features

• Integrated services: email, calendaring, contacts, notes, and collaborative “rooms”
• WebCit web interface for end-user access and administration
• Standards-based access via SMTP, IMAP, and XMPP (Jabber)
• CalDAV/CardDAV-style calendaring and contact access via WebCit (GroupDAV/Webcal)
• Built-in SSL/TLS support for encrypted connections
• Optional text-mode terminal client with a classic BBS-style interface

Use Cases

• Self-managed mail and groupware server for small organizations or families
• Team collaboration spaces organized by rooms (projects, departments, communities)
• Centralized calendars and contacts accessible from compatible clients

Limitations and Considerations

• Full functionality depends on multiple components (Citadel Server plus WebCit for web UI)
• Uses Berkeley DB as the primary datastore, which may not fit environments standardized on SQL databases

Citadel is well suited for users who want a single, cohesive server for email and collaboration with multiple access methods. Its room-based model and broad protocol support make it flexible for both personal and group communication workflows.