BitWarden.

One of the best, if not the best password manager I’ve ever used.

Recently it's been Obtanium, basically it allows you to add apps which are hosted on GitHub/other app sources which don't have auto updating, and have them automatically check and offer to update!

It's been really useful for Lemmy clients (liftoff/Jerboa)/any android apps from:

GitHub

GitLab

Codeberg

F-Droid

IzzyOnDroid

Mullvad

Signal

SourceForge

SourceHut

APKMirror (Track-Only) APKPure

Third Party F-Droid Repos

Jenkins Jobs

Steam

Telegram App

VLC

Neutron Code

"HTML" (Fallback)

Syncthing

It's a decentralized continuous file synchronization tool. It's literally magic.

AntennaPod. The developers seem to have kept it to a very simple remit of just doing podcasts and doing it well.

Simple Gallery, no nonsense gallery app that's pretty fast and has a built-in image editor.

is Tachiyomi open source? if it is, then that. It's always one of the first things I install on my device.

There's just no better manga/comic reader app on Android (even on PC tbh).

The only thing better than Tachiyomi is one of its forks like TachiyomiSY which I'm currently using.

Termux

This app alone is one of the huge reasons why I prefer Android. I love that I can natively run a bunch of Linux utilities directly on my phone and use it like I would a regular computer. Everything from Vim, Python, and various networking utilities, I've played around with so many different tools which has helped expand my skillset over the years.

I also use the Termux-X11 addon to have a full xfce desktop environment running on an external monitor with HDMI out over USB-C.

Phones are quite capable devices and using tools like these really unlocks their full potential.

Firefox by a huge margin, because it's integrated into how I use the internet so well now I don't even notice it's a FOSS app.

As far as more niche apps goes, Joplin. Since they added WYSIWYG editing it's an easy Evernote replacement that just does what I want in a note taker/web clipper app.

I use many, but DAVx⁵ is essential to keep my contacts and calendar in sync.

A few other favourites:

• Mull: a privacy-hardened version of Firefox
• Tasks.org: fantastic task app, works well in combination with CalDAV task lists synced with DAVx⁵
• Syncthing(-Fork) for sharing notes and files between my phone, tablet and computer.

OsmAnd GPS map and route planner.

No bullshit, and it works offline without ever bugging you to download new maps. Great route planner and directions. Simply amazing IMO.

However this is #2 after Firefox, but Firefox is already prominently mentioned.

I have a lot but I’d say Inkscape has to be my number one as a recommendation for something that a lot of people would find useful.

Sorry for my boring answer. Never really thought about it until now. It'd probably be oandbackup.

It allows me to make my phone fully operational, customized to my liking. Including replacing the stock ROM with a custom one, rooting, and installing my favorite apps *with their settings*, in less then 15 minutes.

More recently Habitica and Goodtime have been instrumental in the way that I approach productivity

• Habitica is a habit tracker/to-do list that lets you treat your life as an RPG, and provides me the extrinsic motivation of "I want to level up" that pushes me to accomplish tasks that I otherwise would have been lax on
• Goodtime is simply the best pomodoro app that I've found that has a minimalist interface, configurable timers (on the fly), and robust statistics monitoring (with the option to export to CSV)

In combination they've helped me move my daily focus into more deep and focused work, rather than trudging around and getting distracted by whatever catches my eye

Rethink dns: https://www.rethinkdns.com/

Great features to view internet traffic, customize and block apps

KDE Connect in combination with Valent. The clipboard sync especially is the most useful feature for me. Followed by FairEmail and Syncthing-Fork.

I would've said Infinity for... something, but we know how that turned out. So, I'd say it ir most likely Fennec F-Droid, it is the first app I install in every device that isn't a tablet

Jellyfin! I love having access to my own movies and audio audiobooks wherever I go!

Vim