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4. Screen Sharing

Available on: Mac

When Mac OS X Leopard hit shelves last year, it came with a handy little upgrade in iChat (Apple's homespun AIM client) that lets two Leopard users share screens with each other on the fly.

Want to show your friend or colleague what you're looking at on your display? Just share your screen with them. Or ask them to share their screen with you. It's free. You get an exact view of everything they can see, as well as the ability to control their mouse pointer and click around as needed. It's a great way to fix your mother-in-law's computer without actually having to go visit her. (Not that you would mind, of course.)

Windows Meeting Space, built into Vista, offers similar functionality but only over a local network, so sharing your screen with a remote relative isn't an option. Fortunately, a Web tool called LiveLook allows you to share your screen in moments, no matter what operating system you or your remote pal happen to be running, and it doesn't require an IM session to launch. Just log in to LiveLook.net and click 'Show My Screen'. LiveLook will give you a unique session ID number to share with your friend. When they enter it at LiveLook.net, they'll immediately see your screen. After the 14-day free trial, LiveLook jumps to a hefty $40-per-month fee, or to a pay-as-you-go plan priced at 2.5 cents per minute.

5. Time Machine

Available on: Mac

Apple's Time Machine backup utility is one of the coolest new features in Leopard; with its help, backing up all of your files to an external drive is idiot-simple. Better yet, it lets you quickly recover an older version of any backed-up file, so you can undo all of your horrible, horrible mistakes.

Windows XP, and most versions of Windows Vista, have no such feature. Sure, they have a backup utility built in, but it's nowhere near as easy to work with as Time Machine is, and it will do nothing to help you track down lost versions of your important files. But three versions of Vista (Ultimate, Business, and Enterprise) do come with a utility called Shadow Copy, which lets you retrieve older versions of your files by right-clicking the file and choosing 'Restore previous versions' from the context menu.

What few people know is that cheaper versions of Vista (including Home Basic and Home Premium) do record the necessary data for Shadow Copy to work--they just don't give you access to that data. A free utility called Shadow Explorer can set that data free, letting you roll back to an earlier version of just about any file on your hard drive, without forcing you to buy an expensive OS upgrade you don't need.

6. ISO Burning

Available on: Mac, Linux, PC-BSD

Mac OS can do it. Linux can do it. PC-BSD and just about every other modern OS can do it. But for some reason, Windows can't burn an ISO disc image to CD without a little third-party help.

If you want to burn a CD image on occasion, but you don't want to buy premium disc-burning software, try Alex Feinman's free ISO Recorder. Available for XP and Vista, ISO Recorder adds disc-image burning to your context menu whenever you right-click on an ISO file. It's a lean, simple utility that does just what it's designed for and nothing more. ISO Recorder is available in 32-bit and 64-bit versions for Vista, and the Vista versions support DVD burning in addition to CD burning.

7. Stickies

Available on: Mac, Linux

There's no shortage of applications and Web sites waiting to help you sort through your to-do list--but for my money, nothing beats a good, old-fashioned sticky note for sheer visibility. Macs have long come with an application called Stickies that adds the functionality to your desktop, letting you stick notes anywhere, color-code the virtual paper, and set the fonts to your liking. Many Linux distributions come with a utility called TomBoy Notes, which takes the Stickies idea to the next level by integrating hyperlinking functions that make the notes great for brainstorming, too.

Technically speaking, Windows Vista now includes a similar feature in the form of the Notes gadget in the Windows Sidebar. This widget applet is a poor imitation of its Mac and Linux counterparts, however. For a sticky-note app that really pops, try Stickies for Windows. This simple, free, open-source program lets you customize your notes to your heart's content, and stick them anywhere on your desktop.