Multi-User Dungeons (or simply MUDs) are similar to text adventures in that you type commands, and a description of what happened and where you are comes up on your screen. The major differences between a MUD and a text adventure are that lots of people can be on a MUD at the same time (hence the "Multi-User" part of the name), and also that the MUD's "world" is persistent (things can happen there even when you're not connected). When you first connect to a MUD you have to create a character. Your character will have certain properties, called statistics1 which will affect what it can do. During character creation you have to choose a race2 for your character, which also affects what kind of stats your character will have3. You also have to choose a class4 which will affect what skills you can learn5. After choosing race and class, you then choose a gender6 and an alignment7. Having done all that, you can then optionally elect to pick what skills you want to start off with, or you can simply accept the default skills for your race/class combination and begin playing8.
On most MUDs, the way in which you gain experience points is by "killing" various different monsters. Once you have gained enough experience points, your character will go up a level and you get a chance to improve your stats and skills, using training and practice points9. Training points can be used to improve your stats, and if you save up enough of them you can also gain new skills. Practice points allow you to improve on the skills you already have.
Places on a MUD are divided up into "areas", and to get to different places you need to know the directions10. You can enter directions at the MUD prompt11, your character will move into the next room and you will see a description of the room and what or who is in it. If you see a monster, you can try and "kill" it by typing the word "kill" and then the monster's name. Be warned though - some monsters are quite powerful and may defeat your character very rapidly, so until you've gained a few levels and improved your skills it's best to stay in the training areas12. If you're successful in defeating the monster, you're awarded some experience points, and as mentioned previously when you have sufficient experience points your character will raise a level.
Frequently Asked Questions
Now that you have a general idea of what a MUD is and what you do on one, you might be asking yourself a number of questions, some of which I shall now attempt to answer.
Q: Where do I find one of these MUD thingies anyway?
A: There's a web site called the MUD connector which has a big list of MUDs, together with details about each one and a search engine so you can find the kind of MUD you'd like.
Q: Do I need any special software to connect to a MUD?
A: You need some sort of telnet program. There is one provided with Windows, which you can use, but it's rather basic so you may prefer to download a better one - my personal recommendation would be CRT. There are also programs called "MUD clients" which are more specifically designed for use with MUDs - IMHO the best client for Windows is zMUD.
Q: Does it cost anything to play on a MUD?
A: In general (unlike graphical MMORPGs such as Everquest or Ultima Online) it does not cost anything to play on a MUD. However, that is of course MUD-specific and you should check the MUD's web site beforehand.