Linux

• Distributions: Debian, Red Hat, SuSE, Caldera, MandrakeSoft, etc.
  
  
• X11 - XFree86 : Freely redistributable implementation of the X Window System that runs on UNIX.
  
  Windows Managers:
  GNOME (GNU Network Object Model Environment)
  KDE (The K Desktop Environment Project)
  UDE (Unix Desktop Environment)
  FVWM
  Motiv