Awesome list. Have you found any app for recording calls? (I live in Hungary and receive calls in Hungarian sometimes and would like to record them to translate and understand what the call was about.)
Also, I don't see anything for audiobooks. I use Smart Audiobooks, but was wondering if there are more open source options.
I use Voice by Paul Woitaschek (available on F-Droid). It has a nice, simple interface and a few really useful features. I've gone through dozens of audiobooks in various formats with it and haven't had any problems yet.