The free audio book at ChristianAudio is Augustine’s Confessions.
From the website:
The Confessions is at once the autobiographical account of Augustine’s faith and at the same time a compelling theology of Christian spirituality for everyone. Among the most important classics in Western literature, it continues to engage modern readers through Augustine’s timeless illustrations and beautiful prose. Augustine’s Confessions is a book to relish the first time through and then profoundly enjoy over a lifetime of revisiting
Faith by Hearing 