Linux

Ah, UNIX: the dinosaur of operating systems. (Perhaps a better analogy would be a cockroach: UNIX was here long before DOS and Windows, and - so the UNIX advocates say, anyway - will be with us long after those OS's have suffered the dinosaurs' fate).

I've currently got a freeware version of UNIX known as Linux residing on my hard drive. I don't often use it, in part because I'm more comfortable with Windows 95, and run talk daemons, mail programs, and web servers full-time, but it definitely has its uses - more so when I was taking computer science courses in which I was using UNIX machines constantly, but even now it's a better OS for some applications (Internet-related ones, mainly; I've yet to find a decent desktop publishing program for Linux).