Just stumbled across this on the Audible app.
You can 'Send a book' to a friend and they get a free copy (you keep your copy).
The first book you receive is free. Unlike most Audible offers this works for existing users as well as new ones.
Just click on 'Send this book' from the book's menu and it gives you a URL to share. .
Why not share your favourite book in the comments below?.
For example here's best seller Thinking Slow and Fast for free! http://a.co/0tjWSW4