I haven't read it myself yet so not sure if it definitely fits the theme of this list but I've been recommended Several People are Typing by Calvin Kasulke and I've heard it's written and formatted entirely in Slack messages! Like a modern day epistolary novel i guess haha.

This is exactly the list I've always wanted

I just started Little Blue Encyclopedia the other day and it fits the bill for sure. Most of the story is written as if it was an encyclopedia but with tidbits about the characters lives thrown in now and again as well. :)

This list is perfection. Thank you so much for making this! I have read Murder in the Family, the Mysterious Case of the Alperton Angels, and the Illuminae Files and have now been searching for more books that have a similarly creative writing style, so I will definitely have to give these a shot now!