Darwin Reader!

DuoBook is the reader that lets you both listen to and read your favorite books, keeping track of your place to let you easily switch between reading and listening. Built for audiobook lovers, it utilizes high-quality professional narration rather than text-to-speech. Meanwhile, the reader provides a clutter-free experience to let you focus on the text.

This is an excellent free alternative to the other Daisy book readers out there; currently in development by the folks at BookShare.org.