[KaVir]

Many muds allow a certain degree of player-built content, but such content obviously has to be carefully restricted to avoid upsetting game balance. Of course this isn't true of all muds; I once played a MOO where I was able to add a whole variety of new content - but because there was no combat or competitive gameplay, balance wasn't a concern.

But for those muds with hardcoded mechanics, there are still a variety of ways in which player-built content can be introduced, and most modern muds include at least some of these.

Crafting systems (as mentioned by Ide) are a good example. These obviously vary greatly from mud to mud, but they typically allow players to design (or at the very least customise) their own equipment.

Another example would be the spellbooks in GodWars1, which allow mages to design their own spells. I know other developers have worked on similar approaches, although I'm not familiar with their solutions.

Many muds also allow a considerable amount of character customisation, effectively allowing players to create or customise their own class. The character creation system in ROM is a fairly typical example.

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