One-stop rec shop

Attention all fanfic readers: Hie yourselves over to Snacky’s Best Fic Ever poll to recommend your all-time favorites (any and all fandoms accepted) and read what others consider the best of the best. Guidelines are pretty simple:

Occasionally, I see discussions about how this is the best damn fic ever, and you’d give it to people who weren’t even in fandom to read!

Tell me about the greatest fic, the one you’d give to people who aren’t in fandom (although, I’d think they’d need to have at least a familiarity with the source material, but that’s up to you) and say, “OH MY GOD, YOU HAVE TO READ THIS, IT’S SO GOOD!” It doesn’t have to be anything recent – it can be the first or last fic you read, however many years or months or days ago. If you can’t narrow it down, pick two. And please, feel free to discuss the fic in the comments.