Xerox got xeroxed.

Microsoft did not invent the gui. Xerox invented the gui. Many other operating systems use a gui, but are not allowed to call their product "Windows" without getting sued. Seems a bit two-faced. Maybe the trademark office will get a clue.

More information: http://www.roughlydrafted.com/2007/08/15/sco-linux-and-microsoft-in-the-history-of-os-1980s/