Monster (also VMS Monster) is an MUD-like game developed for VAX/VMS in the late 1980s. It is known for being one of the first multi-user games to feature an early version of what later became online creation.
In Monster, players can "fight, talk, trade items and explore territory together". Game administrators are also able to "create objects, make locations, and set up puzzles for other players to solve". What is notable is that there are no NPCs in the original version of the game.
Technically the game differs from the typical client-server concept: In order to play Monster, each player runs a separate copy of the game. These Monster processes share the same database, a set of shared files. The interprocess communication is implemented with a shared event file. 
The events happening in every room of the game are recorded to the file. Whenever a player character X does something, it gets logged to the corresponding record in the file. The Monster processes run by the other players keep checking the file, and if the characters controlled by those processes are in the same room with X and if something new by X has been written to the event record, they handle the event accordingly, usually by at least notifying the players about it with some output. 
This file-based approach to IPC pretty much makes it so that a single Monster game/world is only playable from a single machine (originally a VAX) or a cluster of machines. Storing the database of the game on a network file system, however, would obviously work as well, making the game available to a much bigger player base.
Monster was developed by Richard Skrenta at the Northwestern University in Illinois, United States in 1988. It was originally written in Pascal for the version 4.6 of the VMS operating system. According to Skrenta, "the second release of Monster was very popular [in the university obviously]", and the players eventually built over 100 rooms for it. In November 1988, Skrenta released the game (the source code and documentation) on the USENET group comp.sources.games. While probably never particularly popular outside the Northwestern University, Monster was a source of inspiration for James Aspnes to create TinyMUD in 1989. TinyMUD, also featuring online creation, became the basis for one of the three prominent MUD branches of the 1990s, the other two being DikuMUD and LPMud.
It is uncertain as to how many sites were eventually running Monster after Skrenta released the files in 1988, or as to how much some of these versions were modified. One variant known to have existed was "Monster Helsinki" developed at the University of Helsinki in Finland. It was released on the VMSnet newsgroups in the early 1990s by Kari E. Hurtta, and according to the accompanying notes, featured at least NPCs, MDL (Monster Defination Language) for programming the NPCs, new commands, and improvements to the I/O routines of the game.
Relevance to Online Creation and Online Building
The first publicly available mud that featured in-game creation of the game content was Monster. 
"Monster allows players to do something that very few, if any, other games allow: the players themselves create the fantasy world as part of the game. Players can create objects, make locations, and set up puzzles for other players to solve. Game mechanisms allow players to:
- Create and describe new objects and locations
- Specify how game objects function
- Provide text descriptions for events that may happen
Further modifications could made via the menu-based Customize command.
For rooms, the name, primary and secondary descriptions could be changed. A mystery message could be added to a room that would be displayed when a magic object was brought into a room by a player. Trapdoors could be created to bounce players to a named exit (triggered by a random chance) or for bouncing dropped objects to another room.
For exits, one could set multiple aliases (i.e. n|north|road) as well as extended descriptions. Player traversal of exits could be blocked or allowed if a magic object was defined on the exit. Success and failure messages for attempted traversal could be defined as well as the messages other players saw when a player entered or came out of an exit. Exits could be marked concealed and/or flagged as doors to require the player to attempt to open a door or search the room for concealed exits.
For objects, one could edit the description, the article to be used with it (i.e. 'a', 'an', 'some'), and an extended description shown upon closer examination. A magic object or magic room could be defined that would allow or prevent an object from being picked up or used unless inside a specific place. Like exits, success and failure messages could be defined for 'getting' or 'using' an object. An object's type could be set which allowed pre-programmed behavior.
Without NPCs, there was no NPC editor and no NPC artificial intelligence.
- Monster on Skrenta's web site – information and the source code of the game
- Play VAX/VMS Monster Online at wopr.adelphos.org
- Bartle, Richard (2003). Designing Virtual Worlds. New Riders Games. p. 9. ISBN 0131018167.
- Skrenta, Rich. "Introduction [to Monster]". www.skrenta.com. Retrieved on 2009-02-09. (Archived by WebCite® at http://www.webcitation.org/5eT4j8eug) Please note that the short ("opaque") form of the WebCite® URL should be used only in addition to citing the original URL in your bibliographic reference. Alternatively, please use the "transparent" (but very long!) WebCite® URL: http://www.webcitation.org/query?url=http%3A%2F%2Fwww.skrenta.com%2Fmonster%2Ffinal.html&date=2009-02-09
- Skrenta, Rich (November 1988). "[Monster's] README.TXT". www.skrenta.com. Retrieved on 2009-02-11.
- "Monster - multiuser adventure game for VMS, Part01/06". USENET (30 November 1988). Retrieved on 2009-02-11.
- Aspnes, James (4 July 1990). "Monster". USENET. Retrieved on 2009-02-11.
- Hurtta, Kari (6 December 1992). "Delta: Monster Helsinki 1.05 to 1.06 (part 0/5)". VMSnet. Retrieved on 2009-02-13.
- Bartle, Richard (2003-07-15). Designing Virtual Worlds. New Riders Games. pp. 9. ISBN 0131018167. Bartle indicates that this facility was present in the earlier, unreleased MUD II software, but that it was removed by version III.