Following through a link from Andrew Otwell’s post on Ning, to see in the comments a bottlerocket from Dav Coleman, perhaps reflecting that providing people with Lego-like code lets them ‘play well’:
“theyâre a bit like descendants of MUDs when you think about it”
Oh my.
Yes.
Paging Yoz to the red courtesy phone.
Petafloptimism 
ITYM MOOning, shirley?
Beat me to it. MOOs are, by their nature, user-extendible, wheras MUDs tend to have a fixed structure. But I’m sure you knew all this already…
Yuh-huh.