One of the best parts of physical books is the ability to share that book with friends. Digital books publishers have attempted to both encourage and limit digital sharing. Amazon allows publishers to choose whether to participate in sharing or not, about 1/3 of Amazon books are ‘lendable’.
Now Audible has started allowing their audiobooks to be shared. The method is more about trying to get new Audible listeners than really facilitating sharing, but the program is worth paying attention to. The program was in beta as Audible OneBook, but is now simply Send your Book. Either in the Audible App or through the browser, you can share one book with any person. Each person must register with Audible to receive a free book. And each person can only receive one free book. But the giver may share their books with as many different people as they want.
Note: Receiving a Send This Book audiobook and registering with Audible is basically the same as a free trial book. If you look around, you can usually find two free book trial. So this is not necessarily a great deal. (Terms and Conditions)
If you are actually interested in becoming an Audible Member, these are better deals. If you just want to get a free audiobook, use a throw away email address, not your main one.