Big Diagonal Chess
Chess variant played on a big square-like board with diagonal square grid. The roles of the orthogonal and the diagonal directions are exchanged.
Otherwise the rules of chess apply, with the following differences:
Pawn's movement and promotion fields
Before and after castling
The bishop's and the rook's role has been reversed: the bishops can move in parallel to the sides of the board (which are diagonals of the grid), and the rooks can move obliquely (which are orthogonal directions in the grid). Therefore the rook and the bishop swap position in the beginning, and the bishop is involved in castling, not the rook. It is however still true that the bishops remain on the same field colour, while rooks do not have this restriction.
Original version: unknown (see the link below); modified version: Uray M. János, 2017.