I have been considering doing this myself. It would be attached to my front fence on my footpath.
I often leave free things on my footpath with a sign. The items are taken relatively quickly and I have never spoken to the people who take them. One person left a note and some cash when I had lots of one type of plant out.
I have been keeping an eye out for a suitable cabinet that would protect the books from the weather, but with glass so they could be seen.
I would like two cabinets, so I could put children's books in the lower one,