[Kereth]

I'm a little surprised by the question as well. My understanding is that most MUDs have always been in constant development. In RetroMUD, for example, where I play most often, players often, when they're ready to retire, become coders themselves, adding more and more features to the game, so we tend to see new areas come in almost twice a month at times, and new guilds, features, and the like pop up constantly. In the last year we've gotten caravan guard quests, capture the flag arenas, unique weapon mods, and a number of new secondary and tertiary guild options, to just name a few and ignore all the expansions of areas and things of that nature.

Other online games, besides MUDs, will also update regularly, often by periodic patches, and non-online games will often release expansions and such things for sale to add to the game after the original release. If you want direct modification, many non-online games have MOD communities of people who create their own adaptations to the games, while MUDs may in some cases have ex-players or current players enlisted as coders in order to expand their content. MMO's and such, however, typically don't enlist their player bases for anything more than just testing of new content.

So. . . yeah, I suppose a little clarification in the question maybe? Thanks.
-Kereth