Steins;Gate, Rewrite Recommendations
Both explore the option of world lines and the whole time travel theory whereby our timelines diverge from one another. Rewrite has superpowers though, if you're into that.
Warning though: If you watched Steins;Gate first, you may not like Rewrite. If you watched Rewrite first, you'll feel that Steins;Gate is much deeper and has better character development. Regardless, both anime are interesting.