Part of about can't-even-count-how-many fandoms:
Keeper of the Lost Cities
Riordanverse (Percy Jackson and the Olympians, Heroes of Olympus, Trials of Apollo, Kane Chronicles, Magnus Chase, etc.)
Harry Potter
Fablehaven (& Dragonwatch) series
Divergent
The Remnant Chronicles
The Hunger Games
Maze Runner
Princess Diaries
Once Upon A Time (This one isn't a book, per se, but it's still amazing and it is a crime not to mention it, considering it qualifies as a fandom)
ACOTAR
Kings of Sin
Caravan (And A Curse for True Love, naturally)
The Cruel Prince
Six of Crows
Powerless
Fourth Wing
Throne of Glass
From Blood and Ash
The Fine Print
Zodiac Academy
A Shadow in the Ember
Dance of Thieves
The Selection
Lightlark
LegendBorn 
The Prison Healer
Shadow and Bone

AND MORE BECUZ LIKE OBVIOUSLY