Yes, I must admit that there are other operating systems out there, and to be honest, they're not so bad. Of course, your Mac is most at home when using its own operating system, Mac OS X, but since the migration to Intel processors in Apple's venerated computer line, the world of alternative operating systems has been forever opened to Mac users. Now you can give the likes of Linux, Windows, Solaris, and even DOS the chance to fly on your Mac, which is what I think they've all secretly wanted to do for the longest time anyway.
Your Mac comes with the best operating system on Earth; I'm sure that's quite apparent to you by this point in the book, if you didn't know this truth before you even began reading. In terms of functions and tasks, there really isn't anything you can do with other operating systems that you can't do with Mac OS X. Let me clarify before some of my Windows-leaning and Linux-loving friends throw this big book across the room. There isn't a task that you can perform on a Windows or Linux PC that you cannot accomplish on a Mac using Mac OS X, but the software or commands you need to perform that task may differ. If this is indeed the case, why would you want to install alternative operating systems?