Update: I’ve given out all of the US codes, but UK residents can still get a full 22-code set—all of my audiobooks—for free from Audible.
You’ll need an Audible account, but you don’t need to sign up for a free trial or enroll in a monthly plan, i.e. no strings attached. Just sign in with your Amazon password to create your Audible account.
If you are a UK resident and would like your own set of free codes, just email me at email@example.com.