Librivox and archive.org are great resources. They provide tens of thousands of public domain audiobooks, read by volunteers, free of charge. Librivox even has an app, but it doesn't quite measure up to the smooth user experience of a Spotify. So, I set out to build a "Spotify for audiobooks".
Oracy works by connecting to the archive.org server to retrieve the audiobook metadata and MP3 files, and it provides a streamlined UI — the user doesn't have to bother knowing about how things work in the background.
Using Node.js, the app calls the archive.org API, and retrieves all the relevant data.
The front end was initially just simple HTML, CSS, jQuery, and Handlebars. Eventually my Booking.com colleague Cipriano Freitas joined the project, and helped me build the web app in React.js.