The iMac operating system (Mac OS X Snow Leopard) comes with a very useful and fun little application called Dashboard. With a single click it brings up utilities (widgets) on your desktop for as long as you need it, then hides them again. It comes with some widgets preconfigured such as a calculator, clock, iCal (today's date) and the weather forecast. A little exploration and you'll find a surplus of widgets for download.
Widgets are only limited by the developers' creativity. You can track how close meteors come to the earth, get Michael Scott (from "The Office") quotes, a NASA Image of the Day, comic strips, recipes, or monitor the status of the Tube in London. There's even a Public Toilet Locator. Not sure why you'd need that on an iMac...
For the more serious minded digital developers, there are widgets for searching Google, PHP.net or GoDaddy available domains, color pickers that provide the hex code for copy/paste, CHMOD and CSS cheat sheets, a JavaScript evaluator, PHP and MySQL date formatters and so much more!
