There are a number of key standards that make up the CalDAV protocol. CalDAV is based on WebDAV which is based on HTTP and it uses iCalendar and iTIP for calendar data and calendar operations.

The IETF has a mailing list for discussion of the CalDAV protocol.

CalConnect has a Calendar Developer Mailing List for discussion and questions amongst calendar developers. The link offers subscription options and a link to the archives.

CalDAV
Other Useful Calendaring Referencess