ZZT was developed by Tim Sweeney for Epic Megagames, nowadays known mostly for Unreal Tournament, in 1991 and was originally distributed as shareware. In 1997, it was declared freeware.
ZZT is sometimes listed as a game and sometimes as a game creation system, which may be confusing unless you understand that there is no essential difference between the two. Every game creation system is basically just a highly customizable game, while every game becomes a game creation system once its mechanics are understood and its file formats documented.
This said, ZZT was intended to be a game creation system, but its sample game, Town of ZZT, is said to be quite enjoyable.
The games you can create with ZZT are of the adventure/RPG kind, with some action elements. The Kroz series might be an example. There is a patch that allows you to use custom palettes.
