The Chrononauts games are unique in that they are are described by a U.S. Patent: 6,474,650, "Time Travel Simulation in a Card Game".
The patent describes the use of cards to create a Timeline of cards, where changing and event flips the card. This may, in turn, trigger other event cards to flip, such that an alternate history is described by the Timeline. All Chrononauts games are based around this Timeline, altering history to achieve a desired goal.