Wikipedia lists them by country, and with pictures, for example

French: [Boîte à livres](https://fr.wikipedia.org/wiki/Bo%C3%AEte_%C3%A0_livres?wprov...)

German: [Öffentlicher Bücherschrank](https://de.wikipedia.org/wiki/%C3%96ffentlicher_B%C3%BCchers...)

and many more countries. They all need a caretaker, or else they degenerate into rubbish.

In France I stumbled upon one during a holiday trip, it was located in an old phone booth. Hmm, I must have a picture somewhere in my photo collection, …