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 It might be a bit ugly or outdated looking, but I'm about that.

Stardew Valley

Templar Battleforce is a great little turn based strategy game with a squad of persistent troops fighting across missions.

Smart audiobook player, fit notes. That's all I got and they're kind of niche

MiXplorer: Tabbed file explorer with many features. You can get it for free from their website, but it's available paid on Google Play.

Symfonium: Music player compatible with many backends, such as local storage, WebDAV, Subsonic (which includes Ampache, Navidrome)

aCalendar+: Calendar app with many widgets. Best part is the persistent notification, which shows what's happening today, and will happen tomorrow.

Cryptomator: Cross-platform file encryption program, also open source.

Cryptomator is a fantastic way to securely upload your stuff to cloud storage providers like Google Drive, OneDrive, etc. In my case, I use it to have an encrypted blob of my stuff with me on a drive when I'm out and about.

They also give you the ability to purchase a license independent of Google Play if you didn't want Google to get a cut.

Threema!

FL studio is pretty good. Got it ages ago and it still gets updates

Others have recommended other file explorers, but I use FX and rather like it.

If your device has stylus support I recommend Artflow for drawing/image editing

If you're a fan of customization and getting your home screen just how you like it, KLWP and Nova Prime.

Nova Prime is a launcher with a bunch of customization options for how your app drawer works, how apps are laid out, how big they are, how folders look, etc. I use it for the fact that i can set folders to have the icon of the first app inside, and a gesture so that tapping them opens that app, while swiping up opens the folder.

KLWP is essentially Rainmeter for Android.

just scrolling trough my phone, here's some I like

app opps - lets you change permissions for apps, handy if you want to have multiple things playing audio or use google photos without it scanning your phone.

calcu - it's a calculator!

simple draw - exactly what it says on the tin

es file explorer pro - versatile, but not bloated

moon+ reader pro - a handy reader for all sorts of docs, including search etc

polarr - a photo editing app with features not a lot of apps have. The devs are pushing some dumb filters tho

handy photo - same as polarr

mx player pro - got videos to play?

poweramp - a music player

poweramp equalizer - is what it says on the tin

sd maid pro - for clearing out old files and such

poweraudio plus - used to be the only app with a parametric equalizer. Now poweramp does too

ultrachron - just a nice timer/stopwatch

unified remote - a remote control app, be careful tho, I doubt this thing is secure

web video caster - also downloads videos from plenty of places

and a couple more apps, where the developer has decided to pull the lifetime license and move to a subscription, even after I had bought it

officesuite pro - it's handy, but f them