On the classic PERQs (1, 1a, 2T1, 2T2), there are
several available  
 OSes.
 Until these have been archived, it is best to say "there WERE several
 available OSes"
 I've archived one or two versions of POS, but that's it so far. 
 
Several PERQ-fanaitcs have readable installation kits for PNX and Accent,
so I think it's fair to say those still exist.
-tony