> What I wanted in MUDs was a simple editor to allow people with little technical skill a means to create a world—or extend an existing one.

Those are MOOs. They're fully programmable in MOO code. Here's the original MOO: https://lambda.moo.mud.org/

There's no point to a MOO other than to be itself, although LambdaMOO does have an RPG system in it you can play: https://en.wikipedia.org/wiki/LambdaMOO

Server resources: https://www.wrog.net/moo/

Programmer's manual: https://www.wrog.net/moo/progman.html

yduJ's venerable duck tutorial: https://jkira.github.io/moo-cows/docs/tutorials/wind-up-duck...