ColorForth is not an OS. For C. Moore, an Operating System is a non-thing.

That's splitting hairs a bit. If I boot into an programming system that lets me operate the computer, I'd call that an operating system. I don't see a significant difference between ColorForth (or other native forths) and e.g. home computer Basics, Oberon or even Lisp Machines.

And more to the point, I wouldn't assume that kOS would be closer to Unix/Windows than Forth/SmallTalk/Mesa etc.

Your definition is simply not usable. By this definition, a bootloader is an OS, the BIOS is an OS, etc. All it needs is to force a little bit the interpretation of "lets me operate the computer". Just because "it" doesn't need an OS to run, it doesn't have to be itself an OS.

I think the issue is that there's no name for that kind of software which are just programs that run on bare metal. So everyone just call it an "OS" - including embedded system software vendors even though what is being sold is really just a library.

But often you have no kernel, no drivers, no resource management, no filesystem, no processes... All features one would expect from an operating system.

Furthermore, operating systems in the generally accepted definition are not supposed to include an interpreter or a compiler. They are not supposed to be interpreters or compilers.

So that's not hair-splitting at all. Those systems are really distinct from operating systems.

Chuck Moore writes one for every project.

That's a deep misunderstanding of what he does. When you run a single process on a single hardware, you don't need an OS.

Slight sarcasm, but he has written several before I'm pretty sure and does deserve his rather mythic status.

Complete USB host driver for Intel EHCI:

  #(*<<#$**$[x;]&^^;

The << idiom really stands out here.