Applications related to gaming: interpreters, game development, etc.

Back in the 80s and in the 90s, game design wasn't something for the common gamer. There were a few programs to help creating games with a decent user interface, aimed at the non-developers, but to be honest there weren't that many.
Interpreters are programs that execute other programs without really emulating the system they were intended to run on. Interactive fiction interpreters, for example, are a must-have for text-adventure fans.