I don’t like the phrasing ‘only you know about’ because that’s not an easy standard to meet, however I have seen a lot of movies…
The Man From Earth (2007) - College professors discuss many topics with a colleague who claims to be thousands of years old. Fully dialogue driven movie shot almost entirely in one room. Great pacing but just a little cheesy in a few spots.
Cube (1997) - Without remembering how they got there, several strangers awaken in a prison of cubic cells, some of them booby-trapped. Also sort of cheezy but quite engaging and dialogue driven. Oddly enough this one was also shot in one room, sort of.
Suburbia (1983) - An overwhelming sense of despair impels a teenager to leave his suburban home and join up with a group of punk rockers. I highly recommend this movie to anyone who has a soft spot for the punk scene of the early 80s..
SubUrbia (1996) - not as good as the totally unrelated 1983 suburbia, but still pretty good - Five teen friends spend their time hanging out behind a convenience store in a sleepy Texas town. This one really reminds me of my childhood, spending all night smoking cigarettes with friends in the parking lot of a gas station, doing nothing, wasting away life.
I’ll add more if I think of any.
I mostly watch old movies these days (40’s and 50’s) and I have a million of those that I love but it’s kind of hard to judge how obscure they might be. People who watch old movies probably have heard of most of the great old movies I have seen.