The board is a parallelogram: each rank's valid range shifts one square to the right. A pawn caught at the edge loses its straight advance and is left with only a diagonal capture.
Said to have been devised by V. Romanchenko, a Russian youth chess trainer, to push his students to think for themselves rather than memorize theory. The ordinary 8×8 board is reshaped into a parallelogram that shifts one square to the right with every rank. Pieces can never cross a non-existing square — this includes a bishop's or queen's diagonal path — so pieces near the board's edge gradually lose their options. The army and piece movements are otherwise identical to ordinary chess.
Simplifications: castling and en passant are omitted. Check and checkmate aren't enforced — capturing the king directly ends the game.