Tiki offers a good mini-calendar (for each user) and a known to be improvable group calendar.
Calendar in the menu, reports tiki activity and can be used for group planning
- don't get confused when looking at future dates and the event calendar is empty... the calendar doesn't realize that you are in Time A looking at Time B... Time B is in the future meaning all of events in Time A are already past and therefore NOT displayed... which can be very very confusing.
- topic images with the calendar do not work
- can not have URLs in the calendar
Ephemeride is global to the website, helps webmaster to choose what to display what day.
UserCalendar is personal and very simple.