linux
I love linux. I hate people that out of ignorance think that linux is an operating system, alas, they are utterly wrong. Thats like saying an engine is a car! Linux is a kernel, the base of GNU Linux which is the operating system!
I don't claim to be a linux expert but I have been using it on and off since 1996 (RedHat 4.0 Colgate). Most of my experience has been since RedHat 9 and onto Fedora Core. I have also scratch built several linuxes.
These days with all the nerffed linux distro's out there that do their very best to be M$ Windows I find the choice getting harder and harder. There are far too many people that _think_ they are linux experts but when you take the pretty GUI away and sit them infront of a console they cant even copy a file. I do all my config from the command line. Even my old favourite Fedora Core is now so bloated and sanitised a simple X install can cost you 2 GiB of space!