Radicale

Radicale is a minimalist CalDAV and CardDAV server that lets you sync calendars, address books, and tasks with standards-compliant clients (e.g., Thunderbird/Lightning, DAVx⁵, macOS/iOS, GNOME). It focuses on being easy to deploy and administer while still providing the core DAV features needed for personal or small team groupware.

Key Features

• CalDAV and CardDAV support for calendars, contacts, and VTODO tasks
• Stores data as plain files on disk (human-readable, easy to back up and version)
• Built-in web interface for browsing collections (optional) and DAV discovery
• Flexible authentication/authorization options (e.g., htpasswd, remote user, custom backends)
• Per-user collections and permissions via configuration
• Works behind reverse proxies; supports TLS via a fronting web server
• Runs as a standalone WSGI application; integrates with common process managers

Use Cases

• Sync a personal calendar/contacts/tasks across phones and desktops using DAV clients
• Provide lightweight DAV groupware for a family or small organization
• Host DAV data in a git-backed directory for audit/history and simple restores

Limitations and Considerations

• Primarily targets DAV sync; it is not a full “groupware suite” (no email/chat modules)
• Sharing/ACL capabilities depend on configuration and client support and may be less ergonomic than full suites

Radicale is a good fit when you want a small, standards-based DAV server that is easy to host, keeps data in straightforward files, and interoperates with many existing calendar/contact clients. It prioritizes simplicity and transparency over an all-in-one collaboration platform.