I developed an idea once.
It was about a scientist in his thirties who had discovered a way to use neutrinos as means of communication. That discovery made the internet much faster and cheaper since you could send information through the earth directly instead of sending it around through massive cables. As a result, he became very wealthy.
He also had a wife and a kid who he loved very much. Basically, he had the perfect life and as a scientist, he had all the money to toy with stuff. That's how he discoveries the possibility for time travel.
After some successful tests that set his doubts aside, he decides to try it. What does he do? The most cliche thing any time traveler could possibly do of course, go back and kill Hitler.
He does, and of course the world is changed drastically. He goes back to his timeline to see the changes, and although his grandfather hadn't been involved in WW II, he still had a kid who was not the MC's father and he never gets born.
He remains in that time period for a little more, trying to understand how he could still exist, but then decides to go back and stop himself from killing Hitler and revert everything back to normal. He goes back a few minutes before he appeared at the spot last time he jumped, but as he waits, his other self never appears. He is confused for a little while, but then leaves back to the future, and Hitler lives.
Again, the world is drastically different. None of the people alive at that point resemble anyone he knew, not even the world leaders. The only ones he is familiar with are those born before he goes back in time.
He panics, goes back again, trying to understand what has happened. During his quest, he finds out that time itself doesn't really exist and that the universe exists in frames, like those of a movie. But after each frame, a whole set of other frames can follow, each one different from the other but all of them possible within the physical laws of nature. The universe is like tree, starting as a single tree trunk at the moment of the big bang, and then branching out. And the timeline of the universe always follows a single branch, randomly selecting which branch it goes through next.
Because of the vast number of possibilities, the MC finds that each time he had timetraveled, he had reset that timeline, and thus even he hadn't changed a single thing, the universe would still end up vastly different from the one he knew. Certain large constructs like the United States and other nations would still exist, but the people that made up those nations would be an entirely different set from those on his timeline, except those born before the moment he appeared.
Then, the MC spends months trying to perfect the timetraveling technique so he can spawn on his own timeline and be reunited with his loving family. A lot happens in between, but in the end, he achieves something very close. He ends up in a very similar timeline to his own, but since the permutations are almost endless, it's still not exactly the one he knew. For all he knows, everything could be the same, but some molecule on a dust cloud a billion light years away could be a millimeter closer to earth.
Thus, his ownself still exists on that reality. In his desperation, he waits for when his own self is alone in his house, goes in, holds a gun against his head, and the book ends.
But I got stuck trying to explain the mechanics of timetravel itself (because it's impossible) and left it like that.