I found a cool little app on F-Droid called Gramophone. It has neat little animations that make me happy, and it can color the player controls according to album art. I’m a sucker for nice UI. I was using Auxio before that. Both are good.
If you want something for ad-less streaming, RiMusic is really nice. For local audiobook playback with chapter selection, Voice is the best I’ve found so far.
I ran into one called SimpleX recently. No accounts or anything and you can host your own chat instance. Downside: The app either needs a constant spot in your notifications or will otherwise only check for messages every ten minutes.
The desktop app is pretty rough to use, as well.