The rook slides along 6 straight directions; the bishop slides along 6 vertex-crossing diagonal directions. The king steps to any of the 6 adjacent hexes or 6 diagonal hexes (12 destinations total). The queen combines rook and bishop. The knight leaps in a hex-adapted L-shape.
Invented in 1936 by Władysław Gliński of Poland. A board of 91 hex cells in three colors, with a king, queen, 2 rooks, 3 bishops, 2 knights, and 9 pawns per side (one extra bishop and one extra pawn compared to ordinary chess). Each bishop is confined to one of the three cell colors, so the three together cover the whole board. Pawns may advance two squares from their starting cell, and capture to the two forward-diagonal cells.
Simplification: the starting array here is an original, symmetric arrangement matching the correct piece counts and movement rather than an exact reproduction of the official Gliński diagram. En passant and castling are omitted. Check and checkmate aren't enforced — capturing the king directly ends the game.