That __is__ true, Doom can run on bare metal, but that's a fairly hacky solution in many ways. Doing it properly in userspace with a LibC and conceptually POSIX

That __is__ true, Doom can run on bare metal, but that's a fairly hacky solution in many ways. Doing it properly in userspace with a LibC and conceptually POSIX syscalls require a bit more effort. It requires a list of LibC functions and POSIX utilities as well as a few OS specific implementations.