At the very basic level, all MU*s are text-based, real-time multi-user interactive systems. In that, they are similar to IRC. However, MU*s generally use the concepts of rooms, items, and players which have descriptions integral to the 'feel' of the game, in much the same ways as the old Rogue and Zork style games do.
As mentioned in the History of MU*s, there are two basic types of MU*s - MUDs, which are descended from BBS games, and TinyMUDs, which were based around a social premise. As a very generalized rule, MUDS tend towards a focus on adventures & quests, with very little social RPG available. Some social interaction and role-play may take place, but that will mainly be an exception rather than a rule. The TinyMUD-descended variations, on the other hand, are generally social or social-RP based, with little to no quest & adventuring involvement. Some of the games are purely social in nature with no role-playing aspects, while others are based on a theme in which players act out their roles. Although the social interaction is quite active on these RP games, players tend to be more reactive rather than proactive. This requires the management to help keep the RP story line moving -- a highly important task on any RP-based game which desires to keep an actively role-playing player base.
How They Work
Each item, room, or player on the server is a point in a database and is referred to as an object. This essay is most concerned with "persistent data" -- that is to say, data which remains in the system across player logouts and system reboots. All of the information associated with the item, room, or player object is maintained in the database record, and is thus available whenever necessary. The means of storage, of course, varies between the different server types.
Access to the server is through a telnet connection. Many different front-end clients for the servers are available, all of which are designed to make interacting with the server both easier to manage and easier to read. These clients give the user a variety of options, including colorization, memorized locations and logins, and frequently used macros.
For the remainder of the overview, a social TinyMUD variation is assumed. Most of the information is applicable across the various servers, but some things are limited based on the server in use or the game itself. When possible some variations are noted.
How To Use
On most games, the potential player creates a login. This login name is referred to as the character the player uses, and will be seen by all other players. All login names must be unique, and the login will only ever have one associated character. The player then has the option of describing herself as she chooses, determining her gender, and applying other basic information, depending on the type of server. On theme-based role-playing games, there are usually guidelines for the character descriptions, based on the theme requirements. Many games now also require a valid email address for player contact by the administration.
Once the character has been set up, the player may then choose to explore the world. This involves sending commands to the server to move from room to room. A room is a type of object which can hold other objects of the player and item types. The room, other options, is able to have a description. This description may be remarkably unhelpful, such as,
Alternately, it may be very complex, including details such as ambient temperature and smell, decorations on the furniture, details about the pictures and their frames, explanations about all of the visible exits and even any noises that are commonly heard coming from other parts of the area. Most descriptions are between the two extremes.
While the descriptions of rooms may include information about furniture, there will not necessarily be furniture objects in the room. Nevertheless, characters are able to interact with the furniture, simply by stating that they do. If there are furniture objects, or other non-player objects in the room, they are considered 'item' type objects. Characters may interact with items by picking them up, entering them, using them, or using commands which may be indicated on the object. Not all of these forms of interactions may be possible, as restrictions can be placed on items by their owners.
Note that characters may interact with other characters by picking each other up, entering each other, or using commands on each other. When available, this type of interaction may be limited by restrictions on the character placed by the player.
To move from room to room, players use exits. Exits are connections between one place and another. They are one-way only -- it is possible to have a connection from Room A to Room B without having a return connection. Usually, exits are made in pairs to simulate a two-way passage. Exits are handled differently from server to server. In some cases, exits are another type of object, while in other cases they are only a shorthand means of calling on the server code. Some may have descriptions or announcements associated with them, while others may not. The use of exits, however, is as a means of getting from one location to another.
Characters may interact with each other socially by speaking or emoting, very much as people do on IRC. Since MU*s are real-time interactive, when someone says or emotes something, everyone in their immediate vicinity who can 'hear' or 'see' will do so. It is then the choice of the recipients if they will acknowledge the other characters.
When a player is finished with the game, they are able to log out and be assured that their items, locations, and descriptions will remain consistent until they next log in (with some exceptions given for game policy). This consistency allows for the illusion of an ongoing world state, which is frequently very important for the role-playing, theme-based games.
As mentioned, the above is based largely on a social type of Tiny. MUDs have a similar structure, although they often have a much different philosophy. One aspect of that philosophy is often displayed in the persistence of items. While the game will maintain character information -- such as name, level, accomplishments, and other character-based data -- it will not maintain any other state. Characters will be moved to a general holding location, weapons and armor may be changed, moved, or destroyed, and entire suites of rooms (areas) may be changed, moved, replaced, or destroyed.
How they are perceived
Please note that the following is, once again, very generalized, and will not hold true across all MU*s! The following is indicating general perceptions and not rules.
While MU*s are all, fundamentally, the same sort of program, the way they are used can be quite different based on the servers. In the TinyMUD family, TinyMUD itself is usually considered a largely social platform, with some small areas available for generalized role-play. TinyMUSH, which has several variants of its own, is frequently used for theme-based social role-playing. These themes can be based on independent ideas, but are usually based on previously published works or role-playing systems. The White Wolf "storytelling" system may be frequently found on "Urban Legend" games, while popular published themes include the Pern novels, the Wheel of Time series, Star Wars, Star Trek and Babylon 5. Other TinyMUD variants include different sorts of role-playing or social interaction. As a general rule, TinyMUDs incorporate social interaction with consensual, social world-building which is largely directed by the administrators of the game.
On the other hand, MUDs are often used as a base for adventure types of games. These games may have some social interaction, but that often may be limited to gathering groups of individuals for a quest. The idea is character progression, where the character increases in skills, abilities, class, or other statistic. While all MUDs of this type do provide "monsters" to kill, some also permit player characters to kill other player characters (PvP). People who are more interested in the social interaction have often been "burned" by PvP, and as a result have given MUDs a darker reputation than they may necessarily deserve. Themes for the MUDs may include all of the same themes as for Tinys, along with the various editions of Advanced Dungeons & Dragons, but as a general rule, MUDs focus on character promotion and adventure, with the world built by the administrators of the game.
MMORPGS are actually graphical variations on MUDs, and have many of the same philosophies and drawbacks which drive the text-based versions. As the graphical games are also usually subscription-based while MUDs are free, changes to the driving philosophies will move these two further apart over the coming years.
The result of the perceived differences between TinyMUD servers and MUD servers is actually a tendency for new games to follow type. Some exceptions will always apply, but those will definitely be the exceptions rather than the rules, and a large number of players will never look for a social role-playing game under MUDs or an adventure, character-promoting game under TinyMUDs. The challenge will be for a new game choosing to cross the perceived server lines is to do so in a way which will attract the wanted types of players for the sort of game which is to be run.