Linux is my operating system of choice. It is adapted from UNIX by Linus Torvalds to run on PC architecture. It is open source software that is available free of charge. The particular flavor that I use is Ubuntu, which is based on Debian's release. The dancing penguin, besides being cool, is the linux symbol. Macs are ok -- after all, OSX is moving closer to UNIX/Linux all the time. Of course, Microsoft is the standard bearer. But I have heard it said that "the day Microsoft makes a product that doesn't suck, it will be a vacuum cleaner". Pretty extreme, and I can't claim it's true, but I have no counter examples.