Not everything you do on your Mac requires a heavy-duty application. For those smaller tasks, Mac OS X features Dashboard. Dashboard provides access to several fun and functional, mini applications called widgets.
Dashboard includes widgets for some of your Mac applications, such as Address Book and iCal, which allow you to access your contacts and view your iCal events, respectively, without having to switch over to the full application. You can add more widgets to Dashboard and even create your own widgets.
To read more about Dashboard, vist Mac 101: Dashboard.