synchronization solution? (Score 2)

One potential solution is to have all keyboard/joystick/etc. input be sent to all the other clients before any of it is handled. (This is like the client/server solution mentioned earlier, but treats everyone as servers.) As long as all the user input is applied synchronously at each client, and each client has the same set of deterministic rules, the game will proceed consistently. If anyone cheats (in any way that causes a change in the actions/properties of the objects in the game) then the game will lose consistency. To check this, simply have each client checksum their data every once in a while. If someone has a bad checksum, throw them out of the game (by a vote of the clients). If someone fakes a checksum, then they can continue playing, but they won't be seeing the same game everyone else is. One advantage of this method is that it does allow modification of the game source, as long as everyone uses the same set of modifications.

There is one game that attempts to use this mechanism (here), but it is incomplete (mostly graphics issues currently). I'm not sure that this approach is viable in practice, but I think it works in well in theory.