The mysterious collaborative feature of iCal hinted at the WWDC keynote seems to actually be CalDAV:

Simply posting your group’s calendar to the Internet is a one-way transaction. Turn it into a conversation with iCal sharing in Leopard. Whether you’ve got an activities calendar or a work schedule, your friends, family, and colleagues can participate in managing the group’s events, thanks to support for the CalDAV standard in iCal. And don’t worry about prying eyes: Security features built into iCal let you control who has access to your calendars.

If this is true, it will be a complete change from the earlier iCal synchronization problems that resulted from Apple trying to push .Mac lock-in. CalDAV is an open standard that any groupware package, OpenPsa included can implement. Let us hope the iCal implementation of it will be open as well…

Updated: OpenPsa already includes a quite competent vCal parser, and using PEAR’s HTTP_WebDAV_Server it is easy to develop DAV features so supporting CalDAV quickly should be feasible. Especially as while we wait for Leopard we can test the calendar sharing features with Chandler.

Updated 2006-08-08: Apple has open sourced their CalDAV server so this really looks like a move to the right direction.