What's a great buy it once Android app?

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.
- I used it to identify the cell towers near my home and turn wifi off when I was out of their range and back on when I was in range. It seemed to help save battery by not constantly looking for wifi networks and I didn't have to remember to turn it off and on manually.
  
  Cell towers are not wifi, but I think I understand what you mean.
  
  That's smart!
  I have a few triggers that turn on Do Not Disturb mode:
  When I open an app that I doom scroll before I fall asleep and when I wake up.
  When I connect to my doctor's or dentist's office wifi.
- There's a completely free app (no ads, either) that prevents auto-rotate from actually happening unless you want it to. It pops up an icon when your phone wants to rotate, and it you don't tap it within the timeout (adjustable up to 3 seconds) then the icon goes away and the rotation never happens. It's highly customizable, and I just can't live without it since I found it.
  
  I also find that super annoying!
  I created a trigger to disable auto-rotate when I'm using the apps I'm usually browsing while in bed (i.e. doom scrolling social media) but I like your idea.
- I migrated to Macrodroid. Much more intuitive and straightforward.
  
  You've reminded me that I have premium from like a decade ago. I should have another go with it.
- What are some things you use it for if you don't mind my asking?
  
  Lots of things
  Change my ringtone based on time/location
  Silence phone if my calendar has the word meet or meeting
  Parse a local news website and read the headlines to me after I dismiss my morning alarm
  Set up car mode if it is plugged in and connected to my car's Bluetooth
  Turn on WiFi based on location
  etc
  
  The main thing is a script to stop any media playing and turn off the screen after x minutes, so I can fall asleep watching YouTube or listening to something. There's probably already an app for that but this is pretty customizable.
  Another stupid use is putting the phone on silent while using the camera app because Samsung won't let you turn off the camera shutter sound.
  
  I've got some that pulls the picture from Bing and the picture from NASA and set them to my wall paper and lock screen back grounds.
  I've got another one that silences my phone when I'm at work or church and not connected to my car blue tooth. I used something similar in college to silence my phone when a calendar event was happening. My phone never made a peep during a lecture! It resets volumes to normal levels after the silent period is done.
  
  I used to get up at 5am and had to get ready for work in the dark so I didn't wake my family. I'm a klutz and fumbling with my phone's flashlight constantly just got annoying.
  I ended up making a little script so that between 5am and 5:30, shaking the phone turned the flashlight on. After 5:30 the sensor turns off to save battery, since I didn't really need it at that point.
  You can do all kinds of handy little things like that
- YMMV depending on your phone manufacturer (or, really, the OS). Some are too locked down to use Tasker, or need annoying workarounds to let it always run.
- I completely forgot I bought that once during a discount, but didn't even have it installed. Started using it now, thanks.

Balatro
- I think my cousin told me he really likes this game. Is it really worth the price?
  
  I didnt enjoy it but my friends that do have lost days to it lol
  
  I got it yesterday, it's bloody solid. Did tend to demolish my battery a bit, but that night just have been because time was dissolving before by very eyes. If you commute or have to burn time a lot (I spent a lot of time in hospital waiting rooms recently) then it's amazing m no microtransactions either
  
  It is one of the best games I've played this year. Really easy to get into for short bits, I pirated it first, played for a few hours on PC, bought it, played it for a few dozen more, and happily bought it for my phone.
  Really good, very addictive
  
  Very much worthwhile. Pick up Slay the Spire while you're at it.

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.
- If you run Home Assistant, Sleep as Android can publish events to an MQTT broker so you can create automations based on those events, like "smart_period", "awake", "not_awake", "alarm_alert_smart", etc.
  
  I used tasker to slowly ramp up my bedroom lights before my alarm goes off. Makes it easier to get up and not as jaring.
- £70 premium version is a little rich for my blood. O_O
  
  Yikes! Is that what it is now? I got it a decade ago for $5.

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.
- Came here for this. Best app I own.

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.
- What are the main things you use it for? All I ever do is change tires and oil. Both my cars are old, but have never broken down.
  
  I'm not the person you replied to, but it's great for telling you why the check engine light is on. If you're somewhere that requires emission testing: you can diagnose if you have an exhaust leak, bad O2 sensor, clogged catalytic converter, etc. Besides that: its good just to know if the check engine light can be safely ignored.
  
  To oversimplify, your car maintains a list of faults, and if that list isn't empty, it'll turn on the check engine light. An obd2 code reader let's you see those codes. I can vouch that these Bluetooth readers + torque are the cheapest way to get these codes without going to a parts store. Even if you have no intention of doing your own work on your car, it's good to have an idea what the problem is so your mechanic doesn't rip you off.
  They generally only return obd2 codes though, which are required by law for emissions. Many automakers keep extra, proprietary codes that require expensive, proprietary tools to read.
- I've started using Piston instead. It's more clean and modern looking and seems to do everything that torque did for me.
- What dongle do you recommend?

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.
- Slay the spire, balatro and Peglin also fit here.
  Amazing indie games, all one time buys.
- I ended up buying it. It's a neat game for sure. Worth at least playing the non paid version.

Symfonium is an awesome music player that's a one-time $5 purchase.
Great question, btw.
- It was the first (only?) app where I was baffled at the features compared to the price. It's a joy to use. If you self-host music, it beats the competition by miles
  
  And the developer is super responsive. I pointed out a bug and once he was able to reproduce the problem, he released a fix by the next day.
  
  I wish sonos had better interoperability, but I did discover if you make a group of speakers and then cast to the "primary" speaker with symfonium, it broadcasts to the whole group.
  Was my only issue with it, but that's 100% a "sonos is shit" problem, not the app.
- symfonium is amazing and id use it if i didnt pay for musicolet
- Trying to use up some playstore credit. I don't have time for a one month subscription, I just want to buy it now and use it later.
- You solved the single issue I had with Finamp: Casting to audio devices.
  THANK YOU

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

Stardew Valley

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.
- Smart audiobook player is great, but I do wish we had an open source alternative. The audiobookshelf app is almost there, but it still requires a self-hosted server I believe.
  
  Smart Audiobook Player is different from Simple Audiobook Player. I actually didn't know about Smart ABP, it looks pretty nice!
  I agree, I'd prefer a FOSS option that's self-contained. The only server I need is one that I can rsync books down from.

Monument Valley. Got the first one for free during a promotion but loved it enough to pay for the sequel and extra levels.
- Wanted to love this but it never seemed to get hard or tricky. Whole game kinda felt like a tutorial for the hard levels they never came.
- This is my partners favourite game.

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.
- I bought moon reader 7 years ago and still use it.
  
  Updoot for moon reader

Smart audiobook player, fit notes. That's all I got and they're kind of niche
- Smart Audiobook Player +1 such a good, feature complete app.
- Fit notes is free? Is it a different one?
  
  You can donate and unlock some things

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.

Buzzkill is good if you have one of those
- Annoying friends who
  
  Send multiple messages instead of just one, Jonny, you annoying cunt

Solid Explorer

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

Others have recommended other file explorers, but I use FX and rather like it.
- Just to mention another file explorer, Solid Explorer is great especially becase it's easy to access Google Drive without having to use the Google drive interface.
- I've been using FX File Explorer since 2012. It's straight up the best file manager on Android, especially when you use SMB and SFTP. Multi window makes moving things around easy as, and the built in text editor works a treat. Being able to share images from apps to FX's "Save As" option is awesome to. It means every app can save where you want.
  No idea why it isn't more popular compared to the alternatives.
- FX is one of the only 2 apps I ever paid for and it's great. I needed something to access SMB shares and it has always worked wonderfully. It's good for poking around in the file system on the phone too. There may be better stuff out since I bought it years ago but I've never had a reason to check.

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
- I will second Moon Reader and Web Video Caster.
  
  So I've used Moon reader pro for several years and love it, but I cannot get reading states to sync between my Samsung phone and Samsung tablet. The book files are named exactly the same on both. I've tried syncing using Google Drive and Dropbox. It treats the books as two separate reading states, though I see the metadata/reading states file edited in Google Drive upon reading for a bit. Any suggestions?
- Thanks for reminding me! I have the free version of unified remote and have been meaning to upgrade.
- Heads up, SD Maid is being rebuilt as SD Maid SE now with more/better features.
  
  Already purchased it. I'm still missing some features, so I currently use both

Threema!
- What makes it better than Signal?
  
  Sign up without using a phone number or email. Threema isn’t trying to shoehorn a silly cryptocurrency project into the app.

Power amp music player

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.

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)
- Qalculate is now on Android.

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

Slay the Spire

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.

Novalauncher Tasker Automate Fairmail
- Nova launcher is a data harvester. You should be aware.
  
  Oh i wasn't... But it's firewalled anyway 😁

MiXplorer - https://mixplorer.com/
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.

Fx file manager. if you do file management locally or want to access SMB share content , cloud, bluetooth etc, this app ia awesome.
- I love it but I can feel it getting neglected with each Android update.
  The worst for me was transferring a video to a computer using the FX Web feature and discovering it silently truncated the video..... when it was already too late.....
- I bought solid explorer at the dawn of android and still use it to this day

FL studio is pretty good. Got it ages ago and it still gets updates
- Just wanted to add that it's a music sequencing/composition/recording tool. I also bought it some 20 years ago and they really delivered the lifetime free upgrade thing - bought some upgrades and plug-in packs now and then nonetheless - - great tool. I feel that presently, I use roughly 20% of its features, but I never find the time to dig deeper.
  edit: refering to the Desktop version

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.

Nova launcher prime
- Not after they have been acquired by analytics company Branch
- Also bought Nova Launcher Prime, but they were apparently acquired in the last year so now Nova is spyware? Anyway, I switched over to Kvaesitso and couldn't be happier.
  
  nova prime + netguard to keep it off the internet has kept me using it. "search focused" launchers are not how I use my phone and nothing else has all the features nova does without being able to just dump the stupid home screen search bar.
- Nova was amazing but they've been bought out. I tried Niagra Launcher and after being frustrated with a new UI, I absolutely love it.
  
  Interesting, i'll have a look on it
  Edit: gave it a try, but you have to remember the exact name of every app, and i dont care enough to remember if the name is 'store' or 'market' or 'app store' for example

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.

Threema.
Neutron music player.
FairEmail.

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

Dicey Dungeons is pretty great.
- Super Hexagon from the same creator is super great/hard.

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

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

OSMAnd+
Symfonium

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

Minimalist phone Launcher that helps to use addictive apps less. And overall a boring home that demotivates you to use your phone.
- Plenty of those for free on F-Droid & IzzyOnDroid.

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)
- There's an open source pdf scanner that works exceptionally well
  https://github.com/Akylas/OSS-DocumentScanner
  
  That's great! It's not super helpful for me, though, since I teach students that often aren't good at troubleshooting technology issues on their own so I need an app that's pretty universal and user-friendly. Plus, the question specifically asked about stuff in the Android play store...
- I was going to mention camscanner, but it’s been years since I was in the android phone, so I wasn’t sure if it’s even still around.

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.
- Subscriptions, no matter how low, are the antithesis of a buy once app.
  Why are you even commenting with this
  
  Because it's supporting FOSS, and it's one of the few foss apps on the play store iirc that let you pay for it.
- Worth noting that it also has a bunch of free alternatives for sync, some self-hostable, and you were talking about the paid service hosted by the Tasks.org devs.

you shouldn't support proprietary software
- It can be open source still though
- You shouldn't tell people not to buy proprietary software
  
  I feel like it's a very important message. You should spread it too.