playBunny: I'd say Dark Chess is different enough from Chess and most of the variants. It takes different skills to play it well. As different as Atomic Chess is from regular Chess, Atomic Chess still requires the same skills to play it well. I don't like Anti-Chess, but it seems like it requires the same skills as regular Chess, you just have to apply them differently. Shogi Chess and Loop Chess might be different enough too. Dropping pieces back on the board is a whole different kind of play. I would certainly put Janus Chess, Grand Chess, Gothic Chess, Los Alamos Chess, soon to be added Embassy Chess, CRC, Fischer Random Chess, Corner Chess, Fortress Chess, and the other games that have the same object but a different set up or board and pieces all in the same category.