An example of games I played that dealt with time travel/machine, not an exhaustive list but I wish I had more time...
ST TNG A Final Unity
The Journeyman Project by Presto Studios
Mission Critical by Legend Entertainment
As I learned more about time and how it can be used, I am convinced a time machine did exist and unexist at one point. In the future, a wormhole will open up to the past and therefore complete the circle of life or the circle of (space*time), a neverending loop. That's why most of these games introduce the concept that aliens from outer space are really us from the future and have invaded the early parts of our lives to complete the neverending loop we find ourselves on.