I asked this question at Stack Overflow but was told it's more appropriate here, so I'm posting it again here.

I'm considering developing a real-time multi-user game, and I want to gather some information about possibilities before I do some real development. I've thought about how best to ask the question, and for simplicity, the best way that occurred to me was to make an analogy to the field (or playground) game darebase.

In the field game of darebase, there are two or more bases. To start, there is one team on each base. The game is a fancy game of tag. When two people meet out in the field, the person who left his base most recently timewise captures the other person. They then return to that person's base.

Play continues until everyone is part of the same team.

So, analogizing this to an online computer game, let's suppose there are an indefinite number of bases. When a person starts up the game, he has a team that is located at, for example, his current GPS coordinates. It could be a virtual world, but for sake of argument, let's suppose the virtual world corresponds to the player's actual GPS coordinates.

The game software then consults the database to see where the closest other base is that is online, and the two teams play their game of virtual tag. Note that the user of the other base could have a different base than the one run by the current user as the closest base to him, in which case, he would be in two simultaneous battles, one with each base.

When they go offline, the state of their players is saved on a server somewhere. Game logic calls for the players to have some automaton-logic of some sort, so they can fend for themselves in a limited way using basic rules, until their user goes online again. The user doesn't control the players' movements directly, but issues general directives that influence the players' movement logic.

I think this analogy is good enough to frame my question.

What sort of platforms are available to develop this sort of game? I've been looking at smartfoxserver, but I'm not convinced yet that it is the best option or even that it will work at all.

One possibility, of course, would be to roll out my own web server, but I'd rather not do that if there is an existing service out there already that I could tap into.

I will be developing for iOS devices at first.

So any suggestions would be greatly appreciated. I think I need to establish the architecture first before proceeding with this project.

Note that darbase is not the game I intend to implement, but, upon reflection, that might not be a bad idea either.