Achron

It's an indie RTS that incorporates time travel. As the general, you exist outside of time and have the ability to observe and direct units during a continuously advancing timeline that includes six minutes of the past and one minute of the future. Events in the past that fall outside this range remain observable, but become unchangeable. Changes to the timeline are updated with "timewaves" (travelling about 3 timeline seconds per real life second) to handle paradoxes. So, you can send a unit back in time to destroy the building that created it, which would mean that in the present the building would trade its existence with the unit every 3 seconds. You can also scout the enemy base, and go back in time to cancel orders to the unit used to scout to save the unit. You can send advanced units back farther in the past where they can do more damage, etc. However, time travel and issuing orders in the past does use up a limited amount of energy that becomes more expensive the farther back you go.

Upon release at the end of August '11, it got a rather poor response from critics. There seems to be a general consensus that while the time-travel gimmick is an amazing experience, the game itself had problems such as with units that are difficult to distinguish visually and awful pathfinding. It's been some time since that, and I think the developers have managed to fix a few of the problems. In particular, they managed to find a bug with the pathfinding system. I'm not exactly sure how much patches and mods have been able to improve on the original product, but the premise is awesome enough for me to hope.