Chess variant played on a circular ring shaped board; as if we had cut a normal chessboard vertically, bent it to a ring and glued it together along the dashed lines.
Otherwise the rules of chess apply, with the following differences:
The rook and the queen is way more valueable than the other pieces, because these pieces can move along very long rings, while the others (e.g. the bishop) can only move to small distances. See also: Value of pieces.
From the basic mates of chess only one works: mating with the queen. All other basic mates require to force the king into the corner of the board, however, this board does not have a corner.
Dave Reynolds, 1983[ChV.com]