Well, 'His Dark Materials' by Philip Pullman is a wonderful parallel universe fiction. It has multiple worlds with different rules and beings. 'The Chronicles of Narnia' can also be considered in a way, as the different lands in Narnia are like parallel universes compared to our own world. Then there's 'A Wrinkle in Time' which takes the main characters through different dimensions that are sort of like parallel universes.
One of the great ones is 'The Dark Tower' series by Stephen King. It involves different worlds and a complex multiverse. Another is 'Sliders', which is about a group that slides between parallel universes. And 'Fringe' also delves into parallel universe concepts with its own unique take on the idea.
Some excellent parallel universe fictions include 'The Man in the High Castle' by Philip K. Dick. It presents an alternate history which is like a parallel universe where the Axis powers won World War II. 'Doctor Strange' in the Marvel Comics also deals with parallel dimensions and universes quite a bit. In addition, 'Cloud Atlas' by David Mitchell has elements that can be related to parallel universes as it jumps between different times and places that seem to exist in different realities.
Chapter 136, "Jiang Li Can Actually Draw Talismans?!", is the clearest early answer because it turns Actually Draw Talismans's situation into a concrete plot event. The chapter turns that into something concrete by moving from A few people retraced their steps back to the place they had just...
Chapter 105, "He Yun, let me give you a reading", is the clearest early answer because it turns President Shang's situation into a concrete plot event. Early on, But this did not elicit any sympathy from the woman on the phone; on.... By the end, However, the next second, things took a turn..
Chapter 138, "From now on, let's get to know each other again", is the clearest early answer because it turns Shu Yan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Is there such a good deal?
Chapter 282, "Whereabouts Unknown", is the clearest early answer because it turns Director Sun's situation into a concrete plot event. Early on, The other villagers quickly heard the commotion and hurried over.. By the end, Why isn't there a live broadcast reporting on their itinerary?]....
Chapter 325, "Miss Jiang, What Do You Think?", is the clearest early answer because it turns Xiao Yu's situation into a concrete plot event.
Chapter 321, ""Great Benefactor" is Jiang Li?!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Several people thus settled down in the living room, and the servants...
Chapter 56, "Popular Host L God Actually Supports Jiang Li?!", is the clearest early answer because it turns Weibo's situation into a concrete plot event. Early on, Lei Shen originally had no idea about the trending topics on Weibo.. By the end, At this moment, Lu Xingchao was still in the dark..
Chapter 52, "Your Child is in Danger Now", is the clearest early answer because it turns Is's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The village chief and the woman behind him exchanged a glance,...
Chapter 303, "Child Disobedient? Pull Down Their Pants and Spank Them Hard!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. It opens with Jiang Cheng felt that Jiang Li had been acting off these past few...
Chapter 346, "Formidable Soldiers and Brave Generals, One Against Three, Reason Behind the Beast Tide", is the clearest early answer because it turns Cold Blood Blade's situation into a concrete plot event. It opens with Subordinate here to receive the order!" After Hou Quan nodded in... and closes on At that moment, the Snowmane King behind also opened its mouth, but....