You can find a lot of exchange platforms for books, audio books, music, films and games online. A few examples:
tauschticket: You will need to pay 0,49€ for one item, in addition to the postage. The currency for exchange is the „Ticket“.
Tausch-Bücher: An exchange platform tree of charge, everything is settled in exchange points from 1-10.
Tauschgnom: Here, items are simply exchanged for others. You can also find „wandering books“ who circulate. Both modes of exchange are free.
Büchertreff: On this website you can exchange, sell or give away books.