An open server distributed with the game, perhaps?

That way, even if the official servers fall, you could still play the game through fansite servers or alone with just your friends. Or single player, even.

The only way I can see an MMO qualifying as DRM-free is if players can host their own servers.

Wouldn't Terraria and Minecraft qualify?

edit: And thinking about it... Sacred Gold probably, as that's practically a MMO. Off hand i don't think Sacred 2 lets you host/server games, perhaps there's a sourceforge project for it...

Server software bundled with the game, so anyone can create one. Characters protected by a password, so you can't play someone else's. No extra checks when creating a character, like cd-keys bound to account.
If possible, allow non-unique character names, and have account name instead.

Basically, how most MUDs work.

Like this? http://www.planeshift.it/

There are a few open-source MMOs like Planeshift above and Eternal Lands which have no DRM. They seem to work pretty much like what JMich describes above.

Last time I played Terraria, it was possible to host my own server, so they would qualify as DRM-free. I'm not sure about Minecraft.

I'm not familiar with Sacred Gold, but if it operates similar to Diablo 2 (not Diablo 3), then that would also qualify as DRM-free. While Blizzard hosted official Diablo 2 servers, players could also create their own servers, and that's the important part. While characters played on unofficial servers were incompatible with the official server, that's not a big deal.

I think your definition of the word 'massive' is somewhat different to mine.
Terraria has a limit of 255 players I think and although Minecraft could theoretically handle thousands of players, realistically most servers can't handle anywhere near that amount of players without lag making the game unplayable.
Sacred only lets something like 16 players play at one time.

I haven't played Terraria (yet), but Minecraft validates your game account against Mojang's master server. You can still play offline if that validation fails (if the server is down, for instance), but I think you can only play locally then. If so, it doesn't really matter if people can make their own servers.

Yeah i guess i didn't consider the sheer numbers... But other than being able to talk to many more people and trading, the massive part doesn't mean anything; Although being able to see someone running by after their next mission or to help their buddies, most groups are probably 16 or less... Or smaller even.

But yeah those are a little small for thousands of players, although having dozens of rooms/servers up at the same time people could come and go as appropriate, to simulate the remainder of the 'Massive' part might be letting all chatting interconnect to groups or all rooms, and being able to see ghosts of players running by who happen to be within 3 screens of eachother with a note on what server they are on...

But that's not quite the same... Unless the player base for a game is so small that you don't need thousands of slots, a few hundred would be plenty for size.

But even the private/fan servers would still have their own DRM, no? You'd still have to log into those servers is what I'm saying, and that would require an account log in.

Ummm not really. Sure having an account/character would sorta be expected, but that's because it's during multiplayer/online play; If you didn't want to worry about saving your progress then it would be more like pogo or kongregate where most of their games you can play anonymously, but you aren't guaranteed to keep any points/achievements you gained. So that's not really DRM not if you can play offline anyways.

Mutliplayer/Online play is the entire point of MMOs... That's part of what MMO stands for: Massively Multiplayer Online. I've not heard of any MMOs that you could play without logging in... But then again, I gave up on the genre a while back, so maybe it's just because I'm ignorant on the matter.