I've had this idea for a game for a long time, ever since I read a synopsys of Timelords (IIRC) by Julian Gollop, which is an old game on the Spectrum. Anyway, this idea is a bit vague, so bear with me. Actually, thinking about it, it's more of an "aspect" that can be "fitted" to any other game that involves time travel. Basically, the player travels in time, and when the affect something, then just like real-life (presumably) they affect it in the future.
To give you a more concrete example, imagine Command and Conquor with time travel. If your units could go back in time and destroy the research centre, then in the future the enemy wouldn't have all the highly advanced technological weapons to fight you with!
Anyway, I'm still trying to think of a good way to actually implement this idea in a game. I'll let you know when I manage it.