  A game-theoretic model of scrip (artificial currency) systems is analyzed. It
is shown that relative entropy can be used to characterize the distribution of
agent wealth when all agents use threshold strategies---that is, they volunteer
to do work iff they have below a threshold amount of money. Monotonicity of
agents' best-reply functions is used to show that scrip systems have pure
strategy equilibria where all agents use threshold strategies. An algorithm is
given that can compute such an equilibrium and the resulting distribution of
wealth.
