It looks like you're new here. If you want to get involved, click one of these buttons!
Either restricted or unrestricted uploads? I suppose instanced zones might be interesting too. Do any games out there do this?
i'm just gonna answer your question as if you were just asking for games that have user created content.
(you were more specific about "uploading", which usually isn't how it works, except for uploading textures in Second Life)
ok, so i mentioned SL already. you can also upload "sculpties" which, if i understand correctly are basically heightmaps (kinda like terrain) that are applied to small 3d objects in order to make the most complex shapes. most of the world is built in-game with "prims". which are basic shapes (boxes, cones, cylinders, etc.) that can be manipulated, cut and twisted. SL is also totally a sandbox world. SL is free, with options to pay for extra features (like more land you can build on).
it is nothing like any other "game" out there tho. its not even a game, but a virtual world that you CAN build games inside of. there's no rpg states or levelling or any kind of "RPG" game mechanics (dice rolling against skills, attributes). but there's a ton of literal role playing. people acting out their online characters.
Wurm Online. don' tknow much about it but i know you can build alot of your own things in it, you can play for free altho you can pay for extra stuff.
Ryzom is also free, but you can pay for extras. they have their "Ring" expansion. at least they TALKED about it. i dunno if it ever went live, but it was a particular area of the world where you could build a certain amount of content. not sure what the limitations were, but i know it wasn't nearly as flexible as SL (nothing else is that i know of (that has any kind of user base) )
i probably forgot something, but that's all i can think of. it will take a long time before most companies have the technology to do this. it almost requires an engine that's designed from the ground up with user submitted content in mind, and hardly anybody thought about UGC until recently.
i don't think any of these world use instancing. instancing is very much against the sandbox paradigm IMO, so i don't understand why you want both.
the upcoming Lego Universe is supposed to allow for UGC (user generated content). no idea about the limitations there.
it'd be a stretch to call Roblox an MMO, (altho there are plenty of asian games out there that are setup the same way that call themselves MMO), but Roblox is about the only thing approaching the flexibility of SL that i know of. like SL, you can make your own scripts to program new gameplay behaviour. as well as making architecture etc.
i want to make my own FPS game eventually that has many UGC features. we'll see how that goes 8)
You can also try "There" - you can make stuff in maya and upload it.
But Lego online sounds like its worth waiting for.
--Note: PlayNC will refuse to allow you access to your account if you forget your password and can't provide a scanned image of the product key for the first product you purchased..... LOL
While it's not exactly an MMO in the truest sense (it is multiplayer), Neverwinter Nights and Neverwinter Nights 2 have amazingly robust tools available for creating player-generated content. I'm a big fan of both of those games, and I've even tried my hand at building some content. Just Google NWN 2 mods/content or whatever, and you'll see what I mean.