The only difference from chess is the initial position.
Played on a rectangular board, but not on the usual 8x8.
Involve new chess pieces not used in standard chess.
Differ from chess in a general rule, like the goal.
The board is still grid-based, but not rectangular.
Played on boards with hexagonal fields.
Played on special boards different from the previous ones.
Chess variants for three players.
Team based chess variants for four players.