I created a register-based VM named RCPU, for educational purposes. You can find it at https://github.com/ddfreyne/rcpu. It has most of what you’d expect from a register-based VM, and even has video output (rcpu-assemble samples/video.rcs and then rcpu-emulate the resulting file with --video).

I intend to write up my findings, but haven’t gotten around to it yet. I do have slides for a talk for this project though: https://speakerdeck.com/ddfreyne/simulating-a-cpu-with-ruby