De Vasa's Chess
Chess variant played on a diamond-shaped board with hexagonal fields.
More details about non-pawn piece movement: Hexagonal chessboards
Pawns move towards the opponent's side, but they can do it in two directions: forward left or forward right to an adjacent field. They capture diagonally forward (in bishop's directions) left or right. They can advance two fields in the same direction from their initial position.
Pawns promote on the opposite edge of the board.
There are two types of castling: on kingside both the king and the rook move two fields, on queenside both pieces move three fields:
Otherwise the rules of chess apply.
Helge E. de Vasa, 1953[wiki]