heh. I had 'Pinball Construction Set' for PC back in the day.

It was interesting in that it used a custom OS. You booted directly from the disk, and it never loaded anything resembling DOS. Went straight into the game. (Well, into a chooser between build and play.) If you tried to read the disk from DOS, it failed to read, saying it was unformatted.

Wonderful copy protection for the time.