Edited from a long page by Marian. For a complete list follow this link to the Ursus page.
This mud attempts to reduce the importance of equipment and stat hunting. The game further focusses on achieving a balance between the various classes, such as there are. Most importantly it means that the game is not allowed to define the character for the player. It also aims to support roleplaying

1. Stats are made relative to their maximum values, and those maxes are not available to players.
2. There are no classes with separate skills, any player can attempt to learn any skill. But at a price. A complicated system requires mastery of certain skills to become proficient in others, and one can't learn a skill beyond the point at which the lower skills are learned. There is also no hope for a player to learn all skills available in the game.
3. Levels are kept, after lots of debating, as a means to show players improvement. But levels are not linked tightly with skills like they are in a standard game.
4. The power of equipment is made relative to the level and toughness of opponents. E.g. a sword does roughly the same percent damage regardless if the target has 10 or 1000 hitpoints. Bonusses are applied directly (or hitpoint wouldn't matter at all)
5. Death is a real prospect, and requires either to restart a character, or to keep stats and skills, but loose ones name

There is more to this mud but I wanted to tell the most significant things here. I also hope I did not make any bad mistakes, some of the stuff on the page was fairly technical. Marian