An online calendar is a great way to let others know about special happenings, like a scrap book or illustrated history.
For example, if you are a sports fan, a listing of your favorite team's schedule is useful not only for you, but for other sports fans on the Internet. Make sure to decide what kind of calendar you want: if it is a personal use calendar with detailed reminders about meetings, you might not want that on a web page that web users can see.