<A HREF="http://www.multicians.org/"
  >Multics</A> is the "great" *(OS) (written in _(PL/I)) whose design began in the late 60's, that meant to become the be-all- end-all of _(OS) technology by having just every (un)imaginable feature, and that was supplanted by _(Unix), despite the fact that Multics was much better(?) designed, because _(Unix)' simple and stubborn design was much more adapted to the very resource-poor architectures of the time.
