ZZT is a text-mode MS-DOS game created in 1991 by Time Sweeney of Epic Games (originally under Potomac Computer Systems). The game consists of several playable worlds, the shareware Town of ZZT, as well as registered worlds Caves of ZZT, Dungeons of ZZT, and City of ZZT.
The name ZZT has no meaning. Its title was chosen so that it would appear last in software listings. A fan backronym suggests that it may stand for "Zoo of Zero Tolerance".
At the time of release, ZZT's graphical capabilities were already rather dated, however the program became a major success from its inclusion of a built-in editor, allowing players to create their own ZZT worlds.
ZZT's financial success allowed Tim Sweeney to continue funding game development and grow Epic into the major gaming company that it is today. If you've ever played an Unreal or Gears of War title, that experience is owed to a little white on blue smiley face that picked up purple keys all those years ago.
What made ZZT such a success was a combination of the editor's ease of use and its inclusion of a basic scripting language known of ZZT-OOP. ZZT-OOP allowed ZZTers to create objects that could move, attack, display text, send messages, and manipulate the boards they were on. Despite lacking what would generally be considered crucial programming language features such as arithmetic support and (non-boolean) variables, ZZT's accessibility to those without programming experience made it a success.
Empowered with the ability to create games and other worlds with ZZT's editor, its community produced more than 2000 titles since 1991 creating games of nearly every major genre. ZZT has seen puzzles, adventures, rpgs, platformers, dungeon crawlers, among others.
After over 25 years, modern technology has made ZZT obselete in many ways. As an MS-DOS program, it can no longer be ran without the use of emulation, either of MS-DOS or ZZT itself. Though the release of games has slowed to a mere trickle of what it once was, ZZT games are still being produced today both by those who grew up among the ZZT community, and from newcomers who have discovered ZZT's rich history and wanted to try their hand at creating something in a both primitive and important tool.
Fortunately to help overcome these hurdles, many people have helped to keep ZZT accessible to a modern audience. A massive collection of ZZT worlds can be played directly in your web browser via The Internet Archive's ZZT Software Library or Chris Allen's ZZT Ultra.
If you'd like to try out ZZT, check out Getting Started With ZZT to get help on setting up DosBox and playing your first ZZT game. For some notable ZZT releases to play, take a look a the Featured Games page.