Name another computer with as many choices of OS and
as many
 versions, including third party and public domain OSs. 
Public domain?  While admittedly I haven't specifically looked, I don't
think I've ever seen a public domain OS for anything, even for values
of "OS" as marginal as MS-DOS.  (Not to detract from your basic point,
which I agree with - if there are public domain OSes out there, I would
expect most of them to be for peecees....)
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