If you're interested in "There" I really recommend "Second Life".
Second Life is the original free-form create-whatever-you-want thing, and I don't think it qualifies as competition for an MMO.??Also, if you like it, it's $10 to join for life, you just can't own land without a monthly fee (though you can rent from other players - Sapling the Evil Landlord begins building 'Reaperslums'

)
Er, nevermind that.??But it is fun, 14 day free trial, and I think anyone should try it (downtime or not) just to see what amazing things people come up with.??You have to remember - everything in the world the users built using the creation tools, except the very basic starter newbie clothing/character customization.
Also, making money ingame is pretty much only limited by your ingenuity and technical savvy with the creation controls (Sapling, the Very Poor weeps quietly).??The physical object creation device is similar to Maya, but doesn't allow some of the more intricate modelling (to keep down on polygons and make things loadable).??Also, objects can be made to perform in certain ways using scripts in LSL (Linden Scripting Language), which is very similar to C and Java.??You can also create your own textures/images in Photoshop or any other picture editor and upload them for a tiny in-game fee to keep people from spamming the server.
Most recently I spent an entire weekend making a tiny pet panda that sits on my right shoulder, and a little glowing ball of light that sits on my left (I call it Tinkerbell).??Tinkerbell flashes, giggles, and flies around randomly if you click on her before settling back to my shoulder.??My next goal is to teach the panda to dance along my arm when I hold it out, then go back to sitting on my shoulder, but I'm still working on learning about joints!
Anyhow, it's good fun, and a nice place to randomly hang out since you can find just about anything.??Also, every character is able to fly and teleport, with a searchable database of different places and activities.??There are some truly amazing architects in the game, as well as people who create vehicles, clothing, and custom avatars.??You can try your hand at making something just about anywhere, and you can store it all in your personal inventory, or carry it around for people to see.
Also, people constantly host free trivial pursuit games, dances, casino games, etc.
Ok, so I sound like I work for the company, but I have never ceased to be impressed by it since I first joined 2-3 years ago.??If anyone reads futuristic sci-fi about the possibilities of virtual reality (a la Neuromancer, the Otherland Series), it reminds me strongly of that within the limitations of present technology (not VR).
*draws in breath*
Anyway, this isn't really a pitch for it during the 4 day downtime, but it is a pitch for it in general.??I sometimes don't play for months, other times I get sucked in.??My name there is Aly Riva.
Edited to note - and yes, with people making anything, there can be some *ahem* inappropriate items, but the areas of Second Life are carefully divided into "PG" and "Mature". I've never seen anything inappropriate cross into the PG areas, since the rules are enforced pretty strictly.