Zero-player game

The term zero-player game commonly refers to games that have no human players, but also to games that have no players at all.

Many computer games can be set up so that the computer plays against itself using artificial intelligence, the canonical example being chess. Since such games already include artificial intelligence, the feature of letting the computer play alone is often added as a gimmick that does not take much additional programming time. In many cases, this can highlight problems with the AI, when all players employ similar strategies. In some computer games, such as the shareware classic "Scorched Earth", AI-controlled players continue playing the game even after all human players have lost.

Entirely computer-controlled games are also frequently used to demonstrate graphics or gameplay, often seen in arcade games where this feature is known as attract mode.

Genetic programming can be used to develop more or less successful strategies against other players through natural selection. Most games used within game theory are zero-player games by the common definition, where many iterations of the actions of simulated players are used to determine an optimal strategy for a particular problem, such as the prisoner's dilemma. The simulation does not need to occur on a computer, but this is common for complex problems with many iterations and strategies.

The movie "WarGames" popularized the idea of using computers to test strategies; in it, a computer which controlled the American defense arsenal played many iterations of a game of "global thermonuclear war" (as well as "tic tac toe") against itself using all known strategies, and came to the conclusion that "the only winning move is not to play."

Classifying programs as games which do not actually have any players is more problematic. "Conway's Game of Life" is perhaps the best known game meeting that definition, along with similar cellular automata, but even here it can be debated whether it is a game, and whether there are players (cells). Complex simulated worlds may generally be counted in this category, such as the computer games "Creatures" and "SimEarth" when there is no player intervention. The classification "evolutionary games" would perhaps be more proper here. Most screensavers are non-interactive, but is arguable for each one whether they are games. The parody RPG "Progress Quest", which plays itself with no human intervention outside some initial choices with no influence in the actual "game", could be considered a zero-player game.

The popular childhood games Candy Land and War can also be considered zero-player games, as their outcomes are determined completely based on the way the deck of cards in each is shuffled, and do not depend on any sort of strategy on the part of the players.

In the same way, some slot machines that require no skill can also be considered to be zero-player games. This would be true of many slot in the USA where no skill is involved and a random number generator determines the outcome of every game. Slots in countries like Japan and the UK, however, often require skill to affect the outcome and the percentage payback, so can not be considered zero-player games.