As in title, preferably open-source, but doesn't have to,
I will start:
KOReader - Amazing reader app, and being able to use the same app across various devices, even non-android ones, is pure bliss. Japanese support is pretty good too, which makes me happy. Though.. Sadly no vertical text support :c
Syncthing-fork - Being able to keep a library of books, and some files, and easily keep the shared folder across various devices, is mega comfy.
Tachiyomi - Cute manga reader.
NewPipe - Really pleasant youtube client, that i sometimes use to listen to things in the background.
Kaku - An useful Japanese OCR app, that works.. quite decently for when I encounter kanji that I do not recognize, and is not text.
EinkBro - A web browser, that on e-ink devices, is quite comfy. Has few... quirks, but works well on e-ink
NetGuard Pro - Allows you to see and control traffic from all apps, so you can prevent data flows to 3rd party hosts like the ones from Google or Facebook. The pro edition is paid and necessary, but it's all open source, just not gratis
Looks healthy. There was activity and new releases in 2021, 2022 and June 2023.
Also, the app might be near feature complete, and if that's the case there will only be sporadic work left like keeping it updated/compatible or fixing security ssues.
I use Carnet for simple note taking and Catima as a digital wallet. Wavelet can be used to apply AutoEq to headphones. The presets are generally really good and make smaller and cheaper earphones sound a lot better than they do by default.
1 for wavelet. They make my Bluetooth headphones so much better. Because it sets a standard EQ it actually makes all my headphones consistent with eachother.
YouTube ReVanced - YouTube with adblocking, SponsorBlock, and Return YouTube Dislike built-in. There is also ReVanced for YT Music.
NetGuard - Firewall that doesn't need root. Works on system apps too so you can help curb the amount of spying done by system apps and apps that don't need an internet connection to function.
Connect - Most functional Lemmy app I could find (and I literally tried them all). Still not as smooth of an experience as Relay, but /u/DBrady has announced no plans to port it to Lemmy so Connect will have to do.
Stremio - Any show or movie you want from any streaming platform (Netflix, Hulu/D+, HBO, Apple TV, etc.), all in one place. The app runs on TVs too. Requires plugins to work, but costs as little as $3/mo or even free, depending on what plugins you use. You'll never need to subscribe to any other streaming platform.
Splitwise - Easily split bills with your SO/roommate(s). Stop arguing over expenses.
Google Rewards - Answer surveys, get Google Play credit. Paid apps are now free!
I've also tried all the Lemmy apps I could find, and must say I'm still the most fond of Voyager. Almost every single time I launch, there's a new update, and new features are showing up extremely fast. Now that there's customizable swipe gestures for all use cases, it's become so awesome to use. I even had an issue with comments getting deleted if I swiped too far while composing, opened a ticket on GitHub, and dev had it fixed within a day. They've just started submitting app versions to to both the Apple and Android store, if you don't want to use the web app.
I second Google Rewards, I also haven't paid for an app for quite some time now. A small note - if it asks if you've visited a specific store recently, the reward is a lot bigger if you say yes, say you bought something, and how you paid. Even if you didn't 😁 There's always (at least) one plausible option, a store you were near, and then a few that look to be fillers. I personally only pick the plausible ones, just in case it's some sort of test. They also rolled out uploading receipts where I'm located recently, and must admit I don't mind Google knowing what I purchased at whatever supermarket.
My problem with Voyager is that it's a web app. It's extremely laggy/unresponsive and the keyboard doesn't work. Firefox doesn't play nice with web apps and I refuse to use any other mobile browser cause I need UBlock Origin and NoScript.
Now that's a great idea. I've been using NextDNS which works quite well and I stay in its free usage cap, but still being self-reliant is better. I'll check that one out.
If you absolutely must get something from Google Play, I suggest Aurora Store, which acts as an alternative frontend for Google Play, so you don't have to have GApps installed.
If you have use for command line programs, Termux, a terminal emulator, is a great option, and it also works with root.
For reading eBooks, I also have a recommendation, Librera Reader (but I'll check the OP's recommendation too).
Material Files and Simple File Manager are great file browsing tools. But if you need a file browser for root specifically, I recommend Material Files specifically.
Good list, but termux isn't a terminal emulator. It's so much more. It's like a virtual machine running cli linux with it's own repos and all. You can have python, gcc, vim, emacs, zsh... you name it. As long as it is tui, it is probably on termux!
Oh yea, Forgot to list Termux, but, since my 10.3" inch e-ink tablet broke, I haven't been using it as often :c
Using emacs inside it, and having lisp.. was mega comfy
moonlight-android - opensource android application to connect to your NVIDIA gamestream functionality provided by most modern NVIDIA graphic cards
I use it often for streaming my computer from my bed to play tactic/mouse heavy games, but latency wise it's very good if using hardware encoding. Less friction than a parsec and/or steam link setup.
Additionally (though I haven't tried it) there is a server software to emulate the NVIDIA(tm) gamestream functionality for AMD/Intel/etc, giving you an open source and low friction way to setup remote game streaming and/or desktop use
https://github.com/LizardByte/Sunshine
Moonlight works great on TVs too! Way better than Steam Link, which can't even display HDR correctly nor run games at framerates beyond 45. With Moonlight HDR works perfectly and I get a silky-smooth 120+ FPS @ 4K.
They fucking better not cause Moonlight is honestly the best way to stream your games to TVs and other devices. Steam Link sucks so badly. It can't even maintain a 60 FPS stream over 2.5G ethernet, let alone 120+.
It might be overkill but Sunshine is the best remote desktop experience I can find on Linux. I used Splashtop on Windows and couldn't find a single thing that actually competed with it's performance until I found Sunshine.
Torque. It allows you to connect to your car's OBD2 port via a cheap Bluetooth adapter. From the app, you can read and clear diagnostic codes, setup custom gauges, and log data. It was very helpful when my alternator was dying and when my car was overheating. I don't have voltage or coolant temp gauges.
I would say.. Termux/SSH clients, as they are text based... Tachiyomi, with disabled animations..
But beside that, not much. I just abuse the fact that e-ink devices that I do have, do refresh the screen at decent speed (e.g Hisense A9, Onyx boox Tab Ultra), so.. most apps are actually useable, even if... the experience on other devices would be pure misery.
Joplin is one of the most important apps I use daily on my Android phone. The desktop version for Linux, an Appimage, synchronizes with the shared database used by the Android app. One can use common cloud services or pay a small fee (now about 18 euros/year) for a specific cloud synchronization service (1Gb).
I stopped using Nova Launcher when it was aquired by an analytics company, since launchers usually have access to a lot of permissions, and I don't trust a company dealing in analytics to operate in good faith with that access.
I have used Lawnchair 2 and recently switched over to Neo Launcher.
Local, SD card, FTP, SFTP, FTPS, DLNA, Dropbox, Google Drive, and about a dozen other cloud storages all in the same place with multiple windows you can switch between so you can easily open two folders in wildly different locations and move files between them as if it was all one big filesystem.
Also let's you host FTP or a webapp from your phone for transfers between other lan devices.
AIMP - best local audio player
Stuff - good simple to-do widget
Hyperlocal Weather - good for cloud cover, not much else
Proton VPN & Proton Mail - VPN is the best free one, mail is secure and well made
Revanced, it's the successor to vanced and just as good. I tried newpipe but I didn't like that I couldn't log in among other issues.
DraStic. I like playing older pokemon game roms on it.
Kanji tree, a great way to practice kanji.
Island, let's me use different accounts on apps that don't allow account switching. For example, it lets me access both my regular amazon account for kindle and my Japanese account that I use to buy manga and books in Japanese occasionally, without having to log in and out all the time. It basically clones apps and let's you open the clone version as a separate app, so you can have the same app open twice with different accounts.
AI enlarger. Just an app that does a good job enlarging images. I usually use it for art so idk how good it is for photos, but I imagine it's pretty good. It does an amazing job with art. Better than most other image enlarging programs or apps I've tried, except for one paid one that I tested with the free points you get for signing up, which was still about the same in quality.
Kiwi browser, works like chrome but let's you use extensions on mobile. I usually prefer Firefox but there are some sites or activities where I really want to be able to use certain extensions and Firefox doesn't have the ability to use the equivalents on the mobile browser. I think Kiwi provides privacy options that help with chrome's privacy issues though, but don't quote me on that.
Oh, I do it a bit differently. I just buy on PC, download azw3, deDRM, then convert to epub with calibre, and yoink onto the devices with syncthing, to read on koreader
Also, AI enlarger seems nice, so I will check it out