I stumbled upon Loyal Books when searching podcast topics. They allow you to stream and download recordings in several formats. I like having them with my podcasts, as I prefer the interface. If you would rather have a dedicated application, Loyal Books offers both Android and iPhone apps.
Recorded by volunteers, quality can vary from chapter to chapter. You can go to the website, or use the apps, to see reviews of each recording. In their defense, I have listened to my share of lacklustre samples from Audible. Audible disappoints less from sound engineering than narrator style or interest. Conversely, the variety of volunteers also supports recording books from over 30 languages. I am now considering using them to brush up on my french, and get exposure to other languages.
If you don’t know where to start, I suggest Meditations by Marcus Aurelius. The entire book is a collection of the Roman Emperor’s journal entries. Most people find him through Stoicism, along with Seneca, but anyone should find his insights fascinating.