Rex Blade: The Battle Begins
Rex Blade: The Battle Begins was this incredible PC game from way back in the day. What happens here is this. It's a standard sort of first-person shooter, like DOOM. Except when you were in the game, you'd actually get to program and alter it! You could sometimes come across computers in the game, with them using REX++ programming language. What could have been a basic DOOM-alike became something that let you make your own games, play a few already built in, and then build up your character's BioStats.