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The very earliest days of the PC revolution were soaked in idealism. People shared their knowledge with one another freely; the very idea of charging for software was an anathema. The early days of the Internet had a similar rosy view of the world.

Today, of course, all that has changed. But there are still plenty of idealists out there, sharing their work with the world freely, and asking others to work cooperatively with them. That's the underlying idea behind the Open Source movement. People create software, and allow others to download and use it freely, and let them modify it as well.

This idealism can create great software. That's where Firefox got its start, for example. But there's plenty of great, free Open Source software beyond Firefox. I've rounded up 20 of my top Open Source favorites. Their sophistication and power will surprise you; you'll find everything from a universal instant messaging program to powerful multimedia and graphics tools, security software, and beyond. The programs show that Open Source adherents aren't wild-eyed zealots--they produce plenty of great software.