From "Wikipedia":http://en.wikipedia.org/wiki/CalDAV http://en.wikipedia.org/wiki/CalDAV :

CalDAV is a proposal for a standard protocol to enable calendar access via WebDAV.

The CalDAV specification was first published in 2003 by Lisa Dusseault as an Internet-Draft submitted to the Internet Engineering Task Force (IETF), and it quickly gained support from several calendaring software vendors. In January 2005 the first interoperability event was organized by the CalConnect consortium. CalDAV does not have an IETF Working Group but the authors still plan to submit it as an IETF standard. CalDAV is designed for implementation by any collaborative software, client or server, that needs to maintain, access or share collections of events. It is being developed as an open standard to foster interoperability between software from different implementors.