Tabletop RPG. It used to be a niche of the internet in the early days, with people posting here and there their scenarios, campaign, ideas etc. It was hard to find and so pleasurable when you found something.
Nowadays it's trusted by ... Wizard if the coast ? Online only platforms and what have you.
I loved #scenariotheque, but now it's almost a ghost website (pardon the french).
I know if sounds like old man yell at clouds, but damn do I miss the early days.