This is pre-Spritely, but in many ways *lead* me to Spritely. I could live hack the game while walking around, but it wasn't safe to let other people add code or contribute. Trying to figure out how to make that safe is what lead me to study object capability security!
You can still see a live demo of me showing this off in a presentation I gave where the slides were the rooms of the MUD itself, and I changed the game in response to player input live! http://gnu.org/software/8sync/