Companion Chess : pieces of same nature don't attack each others
https://www.chessvariants.com/difftaking.dir/brotherhood.html
Crossing Chess = win when the king cross half-board
-Medusa Chess = Isardam
---> à chaque déplacement, check attaques directes + découvertes autour de case de départ dans 8 directions (pas caval)
Kingmaker: pawns can promote also into enemy king
--> no king tracking, getCheckSquares + underCheck test all kings
Eightkings: 8 pawns + 8 kings (non-royal until the last remains?)