Chess Variations

Active Chess [9x8]: Played on a 9×8 board, adding a queen with an extra pawn in front. Invented by G. Kuzmichov (1989), whose students tested the game, deciding that the optimal starting position was to place the second queen on the eighth or ninth files.[4]
Displacement chess [8x8, multivariant]: Some pieces in the initial position are exchanged but the rules remain exactly the same. Some examples of this may be that the king and queen are flipped, or the knight on the b-file is traded with the bishop on the f-file.
 Double Chess by Julian Hayward
Double Chess: Two full armies per side on a 12×16 board, the first to mate an enemy king wins. Pawns advance up to four steps on their first move. Capablanca found the game "remarkably interesting".[5] Invented by Julian Hayward (1916).
Doublewide chess [16x8]: Two regular chessboards are connected for a 16×8 play surface. Each player plays with two complete sets of chess pieces.[6][citation needed]
Endgame chess (or The Pawns Game, with unknown origins) [8x8]: Players start the game with only pawns and a king. Normal check, checkmate, en passant, and pawn promotion rules apply.[7]
Los Alamos chess (or Anti-Clerical chess) [6x6]: Played on a 6×6 board without bishops. This was the first chess-like game played by a computer program.
Upside-down chess [8x8]: The white and black pieces are switched so that White's pieces are on the 8th rank, with pawns on the 7th rank, one step away from promotion. The starting position looks like a standard chess starting position, but from the other player's perspective. As the pawns are blocked by pieces in the starting position, the game always starts with a knight move, and smothered mates are common.[8]