Kontact provides a full fledged and almost complete implementation of the current GroupDAV draft. The GroupDAV connector (called a 'resource' in KDE slang) is part of the KDE-PIM CVS and was released as part of KDE 3.4. Note that the current implementation still has plenty of bugs, pleae refer to the 'groupdav' module in the KDE Bugzilla for more details on this.

The initial implementation of the GroupDAV Kontact resource was done by Cornelius Schumacher and Till Adam. Currently the resource is being maintained by Reinhold Kainhofer.

The Noodle project resulted in the creation of a GroupDAV connector for Evolution. The implementation is not yet well tested, but considered complete.
The first alpha release is available for download: evolution-groupdav-0.1.tar.gz.

The initial GroupDAV connector was written by Alvaro del Castillo of LambdaUX and Anders Carlsson of Imendio. The announcement of the connector is available in Alvaro's blog.
Current development of the plugin is driven by Janosch Rolles and Helge Heß.

Two parallel efforts to implement Mozilla Sunbird for GroupDAV were started in the past, the current status is unknown though.
Yet, right now is probably a bad time to have a ThirdParty work on the connector while Sunbird is being reorganized to support CalDAV. Once complete, the CalDAV connector should be quite easy to tweak to support GroupDAV as well.

Johannes Schneider announced groupdav_sync v0.1, a plugin to connect MultiSync to servers speaking the GroupDAV protocol.

"I'm offering 100$ to anyone who can write a Sync4J connector for the GroupDAV specification. I think this is something that all open source groupware servers need. There is a huge gap in functionality when it comes to syncing. Since Sync4J has the ability to sync with just about everything, a connector for Sync4J will fill this gap. The connector will have to work with any server that properly follows the spec. I put the bounty on OpenSourceExperts.com."

The OGo ZideStore server maps HTTP iCalendar and vCard objects to the internal OGo database and is used to connect various clients. The server currently allows CRUD operations on contacts and events. Todos are read-only (TBD).

The current Citadel server is said to fully support the current GroupDAV draft. The Citadel server directly stores iCalendar and vCards entities as messages in the server and therefore has no data model mismatch.

The SOGo server keeps all internal data as iCalendar and vCard entities and therefore is a perfect match for GroupDAV. Yet the current GroupDAV implementation is untested and probably lacks proper support for HTTP etags.

Ralf Becker added GroupDAV support to eGroupware.

Jan Schneider of the Horde project has started to implement GroupDAV. The current prototype already provides stable read-only support for GroupDAV entities.

The tarent GmbH is adding GroupDAV support to its tarent-contact server. Sebastian Mancke is going to implement the protocol.

Dave Hall - the API coordinator of the phpGroupWare project - announced that he started implementing a GroupDAV server interface.

Martijn van Beers announced a Perl script to add support for the GroupDAV protocol to the Hula server. Currently it just supports one account and is limited to event items (vCard, VTODO and VJOURNAL support is missing). The server plans to implement a full CalDAV server in the long run, so its going to work with GroupDAV clients out of the box (though it won't support address synchronisation).

Adam Williams is currently working on a .NET client

The Kontact connector is implemented as a 'resource' which is a C++ component in the KDE environment and can be reused by other KDE/C++ applications.

The Noodle Evolution connector is implemented as a plugin for the Evolution data server and therefore available to a large number for programming languages and clients in the GNOME desktop environment.

Stelian Pop posted a basic Python GroupDAV client module in the GroupDAV mailing list. The module is based on the Zope WebDAV module.

USA.NET now provides GroupDAV access to their calendaring services, part of their Net@ddress offering.
Read the Announcement!