I love Simple Audiobook Player+. The UI is super minimal (and really maxes out the whole OLED black thing if you choose it) without compromising on features that are kind of essential for audiobooks (e.g. delayed pause/sleep timers, speed settings, volume boosting, an EQ). My favorite thing is the "undo seek" button. I'm an oaf who is constantly inputting accidental touches. When I was using Audible, I'd have to manually find where I was after accidentally hitting the next chapter button or moving the dot on the progress bar. SABP lets me just undo that shit.

It hasn't been updated in a while, but it doesn't need updating when it does its job so well. There are no ads, no marketing notifications, just books. It's like a program from coreutils in app form. It might be a bit ugly or outdated looking, but I'm about that.