iCal

iCal is much more than just a calendar. It allows you to keep track of appointments, both one-offs and ones that repeat, you can set alarms or make additional notes on any entry plus it has a "To Do" section for your important tasks.

Links to Address Book

If you show the birthdays calendar in iCal, it collects its data from the entry in Address book - you cannot alter birthdays directly in iCal.

Synchronising with other devices

It's possible to synchronise your calendars with those on PDAs from various manufacturers e.g. Palm using either iSync (part of Mac OS X) or for more control Missing Sync from Mark Space (see links page.)