Here's a brief introduction for those who have no idea what this is about.
MUSH is an acronym for Multi-User Simulated (or Shared, depending on who you ask) Hallucination. A MUSH is basically a piece of software which acts as a server for a specialized form of communication. Its appearance and behavior depends significantly on the database with which it is run. This database can be modified and maintaned from within the MUSH program itself. MUSH, along with MUX, MUSE, MOO, and possibly others, are derived from MUD, which is an acronym for Multi-User Dungeon, and was originally written quite some time ago. Collectively, this group of programs is often referred to as MU*.
You can access MU* using telnet, which, if you follow any of the links to Shattered Crown, you will most likely use. This is far from optimal, however. There are many applications available out there that act simply as MU* clients. I'm currently working on one for 32-bit Windoze, which, when complete will be available from this page. It will be, simply put, awesome. :) There are others, and they can be found with a relatively simple web search. Once connected, you create, move, and portray your character through the typing of many commands written into the MU* code as well as those written by the builders of the MU*. Probably the most useful command is 'Help'. :)
On a very basic level, MUSH is essentially a game. You create, define, and portray a character through a text interface. In many ways, it is like a piece of interactive fiction. The goal of the game depends primarily on builders of the MU* (those who create and maintain the database). Some MU* are similar to a Dungeons and Dragons sort of adventure where your character simply runs around, kills monsters and opponents, collects gadgets and goodies, and gains experience points (Most often, these are MUD or more direct descendants). On others, the goal is open-ended. Whatever you decide your character seeks is the goal. MUSH (and some others) have left behind many of the hack-and-slash aspects of the original MUD to pursue a more role-playing oriented feel. On Shattered Crown, this is particularly true. There are no built-in commands for fighting, stealing or similar forms of interaction. Everything that happens here is the result of role-playing between characters.
From this description, it may appear to some of you that MU* must be extremely boring. I assure you that it can be as stimulating as you want it to be. If you have an active imagination and are willing to immerse yourself in a character, in a situation, you will find that your imagination is bolstered by others' and that the experience can be both fun and enlightening. I should warn you, though, that it is very easy to become "addicted" to MU*, particularly for those like myself, who had trouble interacting with people face-to-face. You can shed your inhibitions, be a hero or a villain, be a member of the opposite sex, and on some MU* be extroardinary creatures of incredible abiltities.
A MU* is more than a game, however. It's a society. In addition to your in-character role-playing, you will find that you can talk to other players on a more personal level. I have met many good friends initially through MU*. Social interaction is an important part of MU*, and a large part of its enduring popularity. On Shattered Crown, it should be noted, social activity is encouraged, but we ask that it be kept out of in-character situations.
If you are a new to MU* (that is, a newbie), you should be aware that not all players you will meet are honest, kind, or even pleasant. Most of those I've met through MU* have been open-minded and friendly, however. You should also know that characters can bear no resemblance to the players behind them. It can be quite shocking to learn that the woman you've been getting intimate with is actually a man in real life (RL), for example.
For more information, check out the help on Shattered Crown MUSH by typing 'Help'. Or, for a description of MUSH commands and of MUSH building, Amberyl's MUSH Manual.