When two entities interact, there are frequently situations where coordination is useful. However, there is also the possibility that an entity might betray the other, so it's not an optimal algorithm to just assume that other entities you encounter will want to cooperate. The Tit-for-Tat algorithm in the Prisoner's dilemma game gives a good example of an algorithm which can do a good job of cooperating, but isn't particularly vulnerable to betrayals. Unfortunately, the Prisoner's Dilmma game is too limited for Tit-for-Tat to be generally useful. Still, you can see some elements of the Tit-for-Tat strategy in peoples desire for revenge when somebody hurts them.

I think that the largest obstruction to being able to produce something like Tit-for-Tat in a more general case is the fact that in more interesting games we don't have access to complete information. In Tit-for-Tat, if you are betrayed, you know you are betrayed. Furthermore, you know exactly how much you were harmed, and you know you will have an oppourtunity to redress that wrong exactly. In more realistic environments, you are not always certain who betrayed you, or potentially even if you were betrayed. You might not have an opportunity to redress any wrong done to you, and most importantly, you might be in a situation where someone is going to get hurt regardless of the situation.

Two games that I'm particularly interested in, because they are largely, if not totally, driven by social interaction, are Survivor and Diplomacy. The essential mechanic of survivor is that players are gradually eliminated by a vote. Each round, one player is voted off (The TV show had more elaborations, but the vote is at the core of the game). Social interaction is key in convincing players not to vote for you. Diplomacy is a war game, based on WWI. The interesting thing is that it is a 7 player game, and there is no random element. Again, negotiation is key, but Diplomacy is even more interesting, because moves are not necessarily directed solely at one player or another, or even at any player. For more information about Diplomacy, check out The Diplomatic Pouch.

There are a number of general strategies and concepts that seem to arise frequently in games of this type.

Ally

Someone who is cooperating with you. Perhaps because their interests are aligned with yours, perhaps because they've made a commitment.

Promise

People make decisions about how to behave based on how they believe other people will behave. Since players cannot completely predict the behavior of other players (If they could, you could treat the other player as just a piece of the game world, from the perspective of the first player), it is useful for players to exchange information about what they will do in the future. Of course, players are not bound by this exchange of information, so you have the question of whether or not to believe a promise. Note that you can hurt a player by making a false promise, even if your subsequent game move is in no way harmful to them. I could go on, but this is enough for a definition.

Attack

Players can act in ways that are overtly harmful to other players. In Survivor this would be voting another player off. In Diplomacy, it could be besieging their country.

Treachery

Treachery is worse than an attack, interestingly. People get more mad at you if you betray them, than if you act directly against them. The essence of treachery (IMHO - this is getting awfully philosophical :) is deception about your intentions towards the betrayed.

Revenge

I would classify Revenge as going above and beyond a simple righting of the status quo. To use an example from Diplomacy this time, If a country attacks you, it may be the case that your best course of action is to just write off the territory you lost, and go on from there. The impulse to revenge directs you to take back what was stolen, and then take some more. I believe that this is a useful impulse, because punishing people for attacking you will hopefully dissuade people from attacking you in the future. Ideally, you'd like everyone to believe that if they attacked you they would suffer grievously. However, taking revenge imposes a cost on you, as well as the person you are attacking. This is why one of the very interesting questions of the game of Diplomacy is when to take revenge. Some of the best diplomacy players will nearly ignore an attack, and immediately begin negotiating with the attacking player to achieve some other end. This is another definition which is getting to long. I'll get back to this later.

Coalition