[addie.leaderzavos]

I'm looking for a good calendar/appointment tracking application to use alongside OmniFocus. My ideal calendar would be something similar to iCal, but with a multi-level hierarchical structure for calendars like the project sidebar in OmniFocus (iCal's "groups" are not quite doing it for me).

So...
- What calendar-type application do you use, and why?
- What calendar-type application would you recommend?
- What info from OmniFocus do you like to see on your calendar, and how do you get it there?

Thanks!