Real Variants You can play an entire game, and it might even be fun.
SuicideChess? - Same setup as traditional chess, but the goal of the game is to lose all your pieces, including your king. The king has no special value; there is no check. If you can capture a piece, you must do so.
ReverseCaptureChess? - Pieces move the same, but take like the pieces they're attacking. EG, you can attack a bishop with any piece on a diagonal from it, and any enemy piece adjacent to a king puts it in check. If a pawn reaches the opposite side of the board, it must promote. En passant may only be used between pawns.
SniperChess? - Pieces move normally and take normally, but when they take, they don't move: the captured piece just disappears. In a turn, you can either capture or move, but not both.
NuclearChess? - Pawns are nukes. When you take a pawn, it explodes, detonating all the pieces adjacent to it (that is, detonating a 3x3? square with the pawn in the middle), except for the one that just took it--regardless of color.
CylindricalChess? - The board wraps around on the sides.
CornerChess? - The board is placed diagonally and pieces are placed in opposite corners with the king at the far back. Make sure to put the bishops on opposite colors!
Silly Variants Ones that don't work for one reason or another.
ToroidalChess? - The board wraps around on all four sides. Both sides start checkmated.