Circa 2007. I don’t remember which online rabbit hole steered me to it, nor precisely which IF I played first. (I want to say TV Tropes and Shade respectively, but I wouldn’t swear to it.)
I had some earlier experiences with at least one hypertext piece, but I was very young and I’ve never been able to track it down.
The poll at the top of this thread has been open since 2021. Most of the options are for a 5-year period. At the end of 2024, the “2020-present” option will also be for a 5-year period. Should I close the poll at the end of 2024, or leave it open?