Audio Book Versions

For shorter text (up to 20,000 characters/day, or roughly 20 minutes of generated audio), Natural Reader has great voices that can be used for free. The user interface is simple and self-explanatory:

https://www.naturalreaders.com/webapp.html (requires sign-up).

An app to convert entire Pressbooks resources is currently in development — instructions for its use will be included here when it become available.