I find CP/M interesting because it's provably the minimum viable product for an operating system. It was the personal computer desktop operating system that really worked. It came with full documentation, a full development systems (an assembler and a debugger), and a full set of tooling to allow you to port CP/M to new systems. It was portable, too, and you could run the same program unmodified on nearly any hardware which supported CP/M. So it was this great open-ended system, cheap enough to get into the hands of ordinary people, simple enough that you could understand it all, and yet sophisticated enough that, with enough time, you could achieve _anything_ on it...
The CP/M kernel is 3.5kB of 8080 machine code. I think each frame of that video consumed more space than that.