5 dead operating systems, and what their ghosts can tell us

Tremble, mortals! Halloween is upon us. Ghosts, ghouls, and other undesirable creatures are prepared to slink out of their domains and into ours—it’s said that even the dead can rise on Halloween.
In that spirit, let us light some candles, cover the mirrors, and conduct a séance of sorts to call forth the souls of operating systems past. Not so we can gaze upon their ghastly interfaces, but to see if we can learn anything from their digital carcasses and signs of a life well-