Around here, I occasionally find containers labeled 'free books' at garage sales. But, when I travel, I see boxes labeled 'free books', and also see Little Free Libraries.
The Little Free Library came about in 2009, when Wisconsin's, Todd Bol installed one on his front lawn. His was shaped like a school house. Soon after, a nonprofit was founded. Now, there are LFL 's throughout the 50 U.S. states and around the world.
Normally, these feature a small mounted box in a public location filled with donated books. I don't know if you have any near you, but they come in all shapes and sizes. Most are roofed wooden objects sitting on supports on the ground, or mounted to poles. Many are painted with designs.
The Little Free Library in the photo above is stocked with donations. And while it is colorfully painted, I have seen others that are a small wooden box filled with books. Many of the municipal and state parks we have visited have also implemented the 'take a book, donate a book box'.
These exchange boxes, allow the community to be involved in promoting literacy. I know there are people who discard books in the trash once they are done reading them. Donating a book is another option.