Something that haunts me to this day is a program my school used for teaching what I think was phonics or some kind of reading skill. The lessons were accessed by clicking on a door in a dark hallway, in what was probably supposed to be some kind of school setting but as a kid I always interpreted as something much more sinister. The lessons were not any sort of gamified cute thing like a lot of the other educational software I used, they were just on blank screens with a monotone voice over. I was so scared of this program and had nightmares about walking the dark hallways and opening doors to find blank voids. I'm pretty sure the school didn't use the software for long, and I much more clearly remember other, more colorful programs I used more often later.
I've recovered at least some of the other educational software I used in school, but I have never been able to find this one again, since I know so little about it and it was likely only distributed to schools, and possibly not very widely. It's my personal "lost media" mystery.