MOO — Definition, examples, FAQs, and more

MOO: a brief history

The first MOO server was written in 1990 by Stephen White, who built on the social branch of MUDs (games like TinyMUD that emphasized talking and building over fighting). Later that year Pavel Curtis, a researcher at Xerox PARC, extended White’s work into the LambdaMOO server and opened LambdaMOO itself, which quickly became the most famous MOO and the reference version of the software.

Through the 1990s, MOOs spread well beyond gaming. Universities and researchers used them for online classrooms, language learning, and early experiments in virtual community, with projects like MediaMOO and Diversity University. LambdaMOO also became a case study in online governance after widely read reporting on how its community handled serious misbehavior, which shaped early thinking about rules and moderation in virtual spaces.

MOO activity declined through the 2000s as graphical games and the web drew people away, but the software never died. LambdaMOO is still running, and maintained descendants of the original server (such as Stunt and ToastStunt) keep the MOO language alive today.

How it's used today

Today “MOO” usually comes up in two ways. Players use it for the surviving worlds themselves: LambdaMOO and a number of smaller MOOs are still open, and they work much as they did in the 1990s. Developers and hobbyists use it for the server software and its programming language, which modern forks keep compatible with decades of existing code.

You will also see the term whenever people discuss the wider MU* family, since MOO is one of its main branches alongside MUDs and MUSHes. If someone describes a game as “a MOO,” expect a social, building-focused world where builders and programmers shape the setting from inside it.

Types of games where the term is commonly used include:

MOOs, MUDs, MUSHes, and other social text-based worlds

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MOO examples

• A new player types @describe me as "a tall figure in a patched wool coat" so that description appears when anyone looks at their character.
• Someone uses @dig to create a rooftop garden room, links it to their home, and spends an evening writing its description.
• An experienced player programs a verb on a coffee machine object so that typing press button pours a fresh virtual cup for everyone in the room.
• A teacher runs a writing workshop in an educational MOO, with students meeting in a virtual classroom and pinning drafts to a shared bulletin board object.

Myths and misconceptions

1. “MOO” is just another name for any MUD. A MOO is one specific branch of the MUD family, defined by its object-oriented design and in-game programming. Many MUDs share none of those traits, and plenty of text games are neither.
2. MOOs are combat games with monsters and levels. The standard MOO core has no combat system at all. Most MOOs are social and creative spaces, and any fighting mechanics would have to be programmed in by the community itself.
3. You need to be a programmer to enjoy a MOO. Programming is entirely optional. Many longtime MOO players only ever chat, roleplay, and explore, and the simple building commands cover most creative needs without writing a line of code.

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MOO FAQs

What does MOO stand for?

MOO stands for “MUD Object-Oriented.” The name combines MUD, the family of text-based multiplayer games it descends from, with object-oriented, a style of programming in which everything in the world is an object that carries its own data and behavior.

Is a MOO a type of MUD?

A MOO is one type of MUD, so every MOO is a MUD but not the other way around. The practical differences are that a MOO lets players program the world from inside the game, and most MOOs leave out combat and levels in favor of socializing and building.

Is LambdaMOO still online?

Yes. LambdaMOO, the best-known MOO, has been running since roughly 1990 and can still be reached with a MUD client. It is far quieter than in its 1990s heyday, but the world and its community remain active.

Do I need to know how to program to use a MOO?

No. You can chat, explore, and roleplay with plain text commands and never touch code. Building and programming are optional extras, and most MOOs ask you to request permission (often from a wizard) before you can create objects or write verbs.

Can I start my own MOO?

Yes. The server software is free and open source, and maintained versions such as ToastStunt run on modern computers. You download the server, start it with a core database, and connect with a MUD client to begin building your world.