Well, I lumped all the UNIX variants under one hood, breaking out the real wingers, like Mach. I managed these on my list and there are a few that are notably absent (at end).
Unix, Linux, Minux, TOS, OS/9, OS/2, Windows families, Atari TOS, GEM, CP/M, VMS, MacOS -> 8, MacOS 10 ->, DOS, Symbian, PalmOS, AmigaOS, BeOS, APL, PL/1, Forth
Symbolics (Lisp), Multics, JCL, QNX, vxWorks
These last few are really quite interesting milestones or still in heavy use today.
How Many Operating Systems Can You Name?