I was searching through my wishlist looking for the lowest-rated games and this popped up, an old Ectocomp game from 2013.
This is written in pure, raw html, with the only features beyond bare text being hyperlinks and occasional bullet points.
So it is just a classic CYOA-style story with each choice leading to a different webpage entirely, of which there are nine total.
The story is a kind of surreal absurd one where you hear faint music in a hallway but it can spiral into things like being stuck listening to music for a googolplex seconds.
I checked and by the time this came out numerous twine games and other choice-based games had been released, so I wonder if the author just wanted a challenge to try to code something up entirely from scratch. I googled them and it seems like they still do writing now, so that's pretty cool that they've been trying new stuff out for a decade.