Adult IF. There's some incredibly detailed mechanics, but I'll spare the details. And once people couldn't make the mechanics better, they had to focus on plot, puzzles, or images (though puzzles went against the spirit of IF). It got to a point where there were large communities like the roguelikes, awards, and suddenly it collapsed after things got too ambitious or I guess after everyone has seen everything in the genre.

I think there might be a resurgence now or later with Twine and Patreon though.