Entropy is an abstract strategy board game for two players designed by Eric Solomon in 1977. The game is "based on the eternal conflict in the universe between order and chaos [...] One player is Order, the other Chaos. Order is trying to make patterns vertically and horizontally. Chaos is trying to prevent this."
The game originally employed a 5x5 gameboard, but in 2000 a 7x7 board was introduced to allow deeper strategies. Entropy was awarded a rare 6 out of 6 by Games & Puzzles Magazine in 1981. David Pritchard called the game "a modern classic". It is sold commercially under the names Hyle (a 5x5 board) and Hyle7 (a 7x7 board).
The gameboard is a square grid of 7x7 cells. A game consists of two rounds. Each round starts with the board empty, and a bag containing 49 chips in seven colours.
The first player to move ("Chaos") draws coloured chips at random from the bag and places each one on the board in an empty cell. For each chip that is placed, the second player ("Order") may slide any chip horizontally or vertically any distance through empty cells, to rest in a currently empty cell. When the board becomes full, the round is finished, and Order scores 1 point for each chip in any palindromic pattern of chip colors (e.g. red-green-blue-green-red scores 3 + 5 = 8 points; red-red-red scores 2 + 2 + 3 = 7 points) occurring either horizontally or vertically. The players reverse roles and play a second round. The player with the higher score wins the game.
The game has been included as one of the events at the annual Mind Sports Olympiad since its inception. Demis Hassabis had won this event a record five times until losing in 2007. The event has also been won by Hassabis's brother George and by other Pentamind champions, David M. Pearce, Alain Dekker, Paco Garcia de la Banda and Andres Kuusk.