Best if RSS enabled, like Google calendar so updates can be automatically fed into Micorosoft Outlook and online calendars. I don't believe clearwiki would be the primary caledar for people, but it might be for a group. Do not create static calendar lameness like Yahoo Calendar.

We also like calendar functionality to create events and reminders to email to the whole group.

Would also like start dates and due dates from to-do list to appear on calendar.