> Point me to a compiler or interpreter, any of them, that isn't either written in C or written in something that was written in C.
Plenty of languages have self-hosting compilers or interpreters available, which are neither written in C nor written in something written in C.
https://en.m.wikipedia.org/wiki/Bootstrapping_(compilers)#Li...
I'm also pretty sure that some are written in C++, whose implementations are usually also written in C++, and which (while closely related to C) is not C.
> And of course, whatever you play with, it's running on an operating system written in C.
That's obviously not the case if what you are playing with is an OS written in not-C. It's actually not entirely true in plenty of cases, because operating systems that use C range from almost-entirely C (with some assembly) to C-among-other-things (e.g., z/OS and it's mix of PL/X, HLASM, and C/C++.)
> If programming is turtles all the way down, C is the bottom turtle
I’m pretty sure the bottom turtle is native machine code and/or processor microcode.