[doublerabbit]

Engines used to be cool. The original Theme Park engine was it's own application in it's emulator. You had SCRUMM which was another interactive cool thing of it's own. DOS games amazed me as a kid.

[anthk]

The ZMachine it's its own computer too (an emulator in the end).

[iberator]

Probably a simple virtual stack machine. Quite easy to build in ASM and any language.