iCal is an implementation of
iCalendar—an open standard (
RFC 2445) for calendar data exchange. There are lots of other implementations so I'd assume that iCal integration would come first but that wouldn't preclude links to other clients or having a built-in function. I'd be
very surprised if Scrybe wasn't able to exchange data with iCal anyway.
Backpack from
37signals now has a calendar which talks iCalendar, and since I'm a Backpack user my vote would go for integration with Backpack. Scrybe does look very slick though.