What's a great buy it once Android app?

Buzzkill is good if you have one of those

A file explorer allowing for me to transfer files over the network. When Solid Explorer suddenly didn't seem to want to do network transfers anymore (likely because Windows updated something), I waited for that app to update to fix the issue. It never did. I found that MiXplorer was a good alternative that transfers files over the network just fine and works nice and fast as well. The interface takes a bit to get used to (meaning it isn't the same as Solid Explorer) but the app is certainly worth using. Importantly, I can transfer files over the network without issue again.

Notably, this app is free to download (from XDA) however the Google Play version is not free. The Google Play version (which supports development) is a one time paid fee.

Power amp music player

you shouldn't support proprietary software

Square Home.

I know the Windows Phone experiment failed but it was my first smartphone that I bought and not just inherited my dad's work-iPhone when it became deprecated. I really love the "live tile" type home screen and Square Home improves on it as well, instead of just carbon copying it.

Other than that, the FUTO keyboard / voice input and Grayjay, although these three technically offer a lifelong free testing period, similar to WinRAR, but even less obnoxious because they don't even remind you that they want you to pay for them.

Slay the Spire

Balatro

Tasker. Basically an interface for writing scripts for your phone. Even if you don't have a use case in the beginning you'll start finding things to do with it.

Fx file manager. if you do file management locally or want to access SMB share content , cloud, bluetooth etc, this app ia awesome.

Fair Email. I grabbed it from F Droid and paid direct though.

Solid Explorer

I use Paprika 3 extensively.

I find recipes online, download them to the app stripped of all the online recipe bloat. It sorts all the information automatically, including notes and nutritional info. I can check off ingredients and highlight directions, edit tags, compile menus, add my own notes and write my own recipes, it automatically provides a grocery checklist, has a serving calculator to adjust amounts for whole recipes, built in timers, and that's just the basics off the top of my head.

It's free up to a certain amount of storage but I think all the features are available.

the Niagara launcher is still the only app I've bought on Play Store, and I've been very happy with it for maybe 5-6 years now

Sleep as Android

It's just a really great alarm clock app, but with tons of other sleep tracking functionality. I've always had trouble sleeping through my alarms, but I never do with this.

Macrodroid. It is like Tasker, but with a much much better UI.

Torque and a $5 BT car computer dongle. It tells you everything about your car. You can see what warning lights mean and clear the codes.

Read Era is technically free, but I paid for premium years ago and have never regretted it. I can open any kind of uncorrupted book file, from the Amazon reader format to PDF to epub, and everything else I've ever come across. It has a great search function, and the ability to file a book into a custom 'Collection'. You can edit the details of a book, like adding Author or pusblisher info, add your own personal notes to a page or highlighted quote, see an aggregate of all your highlights in a particular file, and adjust the font, background color, and contrast to your hearts content.

I make my whole family use it now, cause I love it so much and Premium works on Family share.

Monument Valley. Got the first one for free during a promotion but loved it enough to pay for the sequel and extra levels.

OSMAnd+
Symfonium

Slice and Dice is a very entertaining one time buy game. No bullshit in game purchases, no ads, I think developed by a singular guy.

Symfonium is an awesome music player that's a one-time $5 purchase.

Great question, btw.

Password Safe Pro
My Expenses
FL Studio, formerly Fruity Loops (also: Desktop)
Threema
Through the Ages (boardgame adaption)

Otherwise, I usually prefer free open source solutions (FDroid), but I regularly donate to keep the projects alive. 1 and 2 are small dev studios that I am happy to support.

Minimalist phone Launcher that helps to use addictive apps less. And overall a boring home that demotivates you to use your phone.

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.

Nova launcher prime

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

Tasks.org is a wonderful open-source todo/task app, that has a low-cost monthly subscription to use it's syncing ability. It's worth it to support FOSS wherever we can.

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

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.

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

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.

Threema!

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

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

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

HiPER Calc Pro. A great scientific calculator I use constantly. (There is also a unpaid, ad-supported version, and the ads weren't too intrusive the last time I tried it)

Dicey Dungeons is pretty great.

Game: crying suns It's a full ftl type game that's on steam as well. Big story. Took me a while to get through it

CamScanner (intuitive and powerful scanner app that processes images exceptionally well and interfaces cleanly with all sorts of other apps) and Hiper Calc Pro (scientific calculator that shows you your input and looks like a classic calculator interface)

PhotoPills

Invaluable as a photographer. I think it's closed source though which is a shame.