LibriFox brings LibriVox.org’s public domain audiobooks to Firefox OS phones as a native web application. It makes use of JQuery Mobile, ECMAScript6, HTML5, and CSS3 and is unit tested via the Mocha test runner framework.
I developed the app under the guidance of one of my teachers, a proponent of Free Open Source Software (FOSS) who wanted an FOSS-compliant audiobook app for his Firefox phone. Although Firefox OS is now defunct, the app largely uses web standard technology, and could be ported to other platforms fairly easily.
It’s listed on the Firefox Marketplace with a 5 star rating!