Timeline (1985)

A "time-travelling" 4-dimensional chess variant played on a grid of 16 miniature chessboards. Each player has 2 rooks and 2 bishops, each in its own warm or cool color. As each piece moves, it literally leaves a paper trail of cardboard chits showing its progress through the game. A piece can be captured at any point on its timeline by landing on a square containing a chit, and any actions taken since then by that piece are reversed. In this way a piece can capture an opposing piece 'earlier' than when that piece captured a friendly piece, thereby returning the friendly piece to the board. The game continues until all four opposing pieces have been captured.