The other day, I sold some wallpaper samples from my flailing Etsy store. Because I didn't have an envelope for the samples, I folded the the samples into some wallpaper and made my own wallpaper envelope. All of which reminded me of Bookswapper.de.
Today there are digital books and Kindles and iPhones, but way back when (TEN years ago, that would be, when I lived in Germany), these options were a lot less common and finding English language books in Germany, especially recently published books, was challenging. However there was Bookswapper.de. You could list your English language books and then swap them for other English language books. The system worked such that each time you sent a book to someone via German Post, you got a point in the Bookswapper system which you could then use to request a book from someone else. The book's first owner paid the price of mailing the book to the second owner. It was a relatively small cost because you could send everything media mail. Also, the cost came back when you requested a book and someone else paid. The whole system worked really beautifully. (And it didn't hurt that we lived across the street from a post office.)
It was always such a cool thing to receive something free in the mail. It was cool to send a book away, as well. I never resented it. I always enjoyed wrapping the book in some old wallpaper, in the coolest package I could make, hoping that the recipient would enjoy both the book and the packaging. It was such a small thing, and yet it gave me such pleasure to be part of this tangible community. Sometimes, I still miss it, even though I now have access to all the English language books my heart could desire.