Look into Mac Ports, most linux donkey do run on OS X with some work. I had KDE installed on my Mac a few years ago. It will not replace OS X, but run on top of it. It's more of a Finder replacement. GTK also works in OS X and a lot of Linux have been ported to OS X. Mac Ports in source based so it will compile everything from source, kinda like Gentoo does. It's a bitch, it takes hours to install something like KDE, and it will never be like a Linux deskop.