What about Mac and Linux?
Other operating systems have been out there for a very long time, but they don't have the marketing power that's behind Windows. I'm familiar with a few, and I'll try to cover the basics: The Mac and Linux.
Mac's are put out by Apple, and have some of the most worry free computer experiences a user can buy. There is a catch, of course, they're more expensive. They're great little workhorse machines, and they can be easy to use. Mac has its share of mishaps. Once I had upgraded a machine to OS X, and it rejected the extra memory that had been put in because it was not purchased from an approved manufacturer. Proprietary hardware and software don't always play nice. If in doubt, it's always fun to go to an Apple store and experience the buzz and vibe you'll get from those folk. Really. You should check it out. If it's worry free computing you're looking for then a Mac is hard to beat, but you pay for it.
Linux has been around for a long time too, but it has only recently come into offering everyday users a trouble free experience. It is true that Linux was the OS for computer geeks around the world to tinker with and make their own. Due mostly to those efforts, there is now a Linux version that can be used by novice computer users. Actually, there are many versions of Linux, or flavors of Linux, usable by everyday people, and most of those flavors are available for download at no charge. Ubuntu is very friendly flavor; You can even try it without altering your computer.
A rising star, Zorin OS, looks and feels like a great computer experience.