Chrononauts is a card game about time travel, that manages to create a complex interaction of events/cards through simple rules. I particularly like the fact that each player has their own goals to achieve through manipulating the same timelines as everyone else!
I love the theme of this game, but I think the mutliplayer game suffers from a couple mechanics that seem a bit tacked on. But I really enjoy the solitaire game, which dispense with the extra stuff and pares it down to the central theme of manipulating history to get back to the alternate timeline your character originates from.
Chrononauts is a very fun light weight game of "what-ifs." The theme of the game is very interesting, in that you're trying to fix the mistakes of other time travelers. The game allows several different ways to win. Usually a good tug-of-war ensues, as players battle over highly sought after events/years. It supports 1-6 players. Enjoy!