Prisoner's Dilemma. In this game, which represents the basic structure of collective action problems for the provision of public goods, each actor has a dominant strategy not to cooperate, leading to an inefficient outcome in which all the participants are worse off than if all cooperated.
Tit for Tat. The strategy of starting to cooperate and doing unto others as they do unto you can lead to sustained cooperation. Mutual cooperation is more likely the greater the uncertainty as to the length of the collective relationship and the higher the number of interactions.