another example of this phenomenon are "free" markets in prisons, where the currency is usually cigarettes.
Other places where freedom is limited have similar characteristics, I remember that we had a sort of food market when I was a child at a boarding school.
As a side note, France has a thing called “fiscal stamps” (timbres fiscales) which I had to use to pay a ~60€ government fee of some sort. One time I did it I paid online and got an A4 thing I needed to print out, which, OK, sure.
The other time I couldn’t do that for reasons I don’t remember and paid cash at a store to get one. What I got was a tiny thing that looks exatly like a small postage stamp of the standard almost-square shape (which is itself funny because all the actual French postage stamps I used were twice as large) except it cost the aforementioned ~60€. Needless to say, I was terrified I’d lose it the whole hour or so before I handed it over to a clerk.
Wikipedia tells me this was a common approach once[1].
Other places where freedom is limited have similar characteristics, I remember that we had a sort of food market when I was a child at a boarding school.