I'm just finishing up another reread of the Dangerverse series, a long-form Harry Potter fanfiction which explores what might have happened if Harry hadn't grown up alone with the Dursleys. Originally intended to be ten chapters of fluff (Harry gets saved by his babysitter, Hermione's older sister, who marries Remus Lupin who then helps her rescue Sirius Black who reconciles with his fiancée…they all defeat Voldemort, whoosh, bosh, the end 😛) it took just a smidgeon over ten years to complete and ran to five volumes which we calculated contain more words than the original 😎
There's so much to explore which would be massive spoilers—the podcast interview with the author hiding under a desk saying over and over "I have been lying to you all this time" lives in blessed memory—and when we found out just how extensive her lies had been, we were blown away. It all stems from one throwaway scene in Prisoner of Azkaban which hardly anybody bothers to remember 😵
Notable is the number of alternate-alternate universes which this one spawned: there's an excellent spin-off called Be Careful which picks up right at the start of Deathly Hallows and postulates the effect of giving Draco Malfoy a chance at a very late redemption…I could go on, and will at the slightest provocation 😱
I don't know of any other HP fanfiction which is as long or as complicated (or complete, for that matter) but if anyone has any recommendations I would like to hear them.