When it comes to desktop operating systems, there are three obvious choices: Windows, Mac OS X, and Linux. But a whole world of alternative OSes lies below the mainstream radar.
These little-known products are actively or recently developed, and some folks actually use them to get things done. Here are twelve of these strange beasts, all of which run on modern x86-based PC hardware, and many of which can be downloaded for free. Impressively, none of them are based on Linux.