Reminders that know where you are
Likewise, iOS's Reminders has come to OS X Mountain Lion. iCal (now called Calendar) used to manage to-do items, but no longer. Now it's Reminders' job. Reminders works like Notes in that it syncs its tasks via compatible servers to compatible apps on any platform.
But Reminders offers some special capabilities, such as location-based to-do items (for example, alerting you to get milk when you leave the office, or to pick up both kids when you arrive at the school).