ZZT (1991)

ZZT is a 1991 action-adventure puzzle video game and game creation system developed and published by Potomac Computer Systems for MS-DOS. The game was later released as freeware in 1997. It represents an early example of a game that allowed players to edit using object-oriented programming. Players control a smiley face to battle various creatures and solve puzzles in different grid-based boards in a chosen world. It includes an in-game editor, allowing players to develop their own worlds while using the game's scripting language, ZZT-OOP.

The game was followed by a sequel, Super ZZT (1992). Other ZZT worlds were published later that same year as Best of ZZT and ZZT's Revenge.