I am still getting organised -- new machine, new AOS-5.1 copy &c -- so could have missed an existing set of the icons I have in mind, but how about some representing operating systems back to CP/M?
CP/M : interlocking chiselled-stone gear wheels with a flint axe leaning against them.
DOS : an ox cart loaded with jumbled letters & digits, towed by bullocks.
UNIX : stacked USian phone books (inc. a C manual) topped by an old button-dialler phone (courteous AT&T reference).
Linux : not sure -- try a parody of UNIX, a heap of paperwork with varied designs of phone & computer having a slightly homebrew look.
OS/2 : (proving we can take jokes as well as dish 'em out) old OS/2 logo backed by a radiant rising sun.
Windows -- abandoned versions : a garish multicoloured Windows logo, one numbered pane broken.
Windows -- current : blue (?) Windows logo fronted by a cowpat/cowflop with a version number on it. (Okay, getting a wee bit political there...)
eCS : the basic eComStation logo.
AOS : today's logo, possibly without version number.
Other OSes (Mac, Beos, &c) : have fun being inventive.