Still working on this. Groups security is tough to translate that properly to who can see what in different categories of data on the calendar.
Meanwhile, here are some examples of good calendar implementations in PHP that are a good guide for featureset:Kronophobia
- School oriented, good GUI, groups (+), SSL (+)PHP iCalendar
- iCal, interoperability (+), Groups (+)WebCalendar
- Our favorite, looks quite mature with Groups (++) but complex, with good import/export possible Palm synch coming soon which we value