I've always felt SIMH was pretty cool. I haven't done anything with the VAX emulators, but a few years back I had a PDP-11 simulation running on a Raspberry Pi

I've always felt SIMH was pretty cool. I haven't done anything with the VAX emulators, but a few years back I had a PDP-11 simulation running on a Raspberry Pi with RSTS/E 7.0. This was roughly equivalent to the system I used in high school, and I laughed out loud when I discovered that 7.0 wasn't Y2K-compatible. The math teacher who taught the computer classes was warning us about two-digit year values back in 1981!