If you're looking for manga similar to Steins;Gate, you might like these titles. All recommendations are made by Anime-Planet users like you!
Hatou Gaku has a very odd friend at school named Marii Yukari. Yukari has purple eyes and a bizarre way of looking at the world: she sees all living things as robots. This has not always worked out well for Yukari, even costing her a best friend when she was younger. However, Yukari insists that the things she says she sees is true, and her vision seems to give her insight into the abilities of others. Gaku thinks she's just weird, but she soon realizes that Yukari has unexpected talents. It seems she can fix anything, and even the police come to hear her insights. It turns out that Yukari's purple eyes are not unique in the world! However, there is one important distinction among those who see humans as other objects. Do humans appear as unimportant as objects, or do those objects appear as important as human beings?
Both of these series can be heavy on the science, both real and pseudo. They both have emotionally charged stories that are told through things such as timeskips, parallel worlds and alternate realities. Both can be confusing at times as the technical jargon piles up, Qualia in particular can get extremely difficult to process at times, but it's never confusing for confusing's sake, everything has a reason or purpose for being there.
If you enjoyed the scientific aspect of either series, then the other is sure to hold some enjoyment for you.
Both sci fi manga based on light/visual novels where the MC have the ability to jump in different timelines (parallel universe) to change and fix the past.