Some of them are not underrated, but I’d just share my favorites…

• AntennaPod for podcasts.
• Aurora Store if you need some Google apps to be updated.
• Binary Eye is a nice and slim qr code scanner and generator.
• CriticalMaps is a good tool if you’re into critical mass events.
• GadgetBridge can be a companion app for your smartwatch (if you have the right one).
• GPS logger just logs your position in an interval you can set. I use it to track my movement in 30min bits.
• GymRoutines is a privacy friendly gym exercise app with a database of your progress.
• K9 mail (soon to be rebranded as Thunderbird mobile) is a powerful mail app.
• KeePassDX is an android password manager compatible with keepass files.
• LibreTorrent is a nice way to torrent your favorite linux distros while on the go.
• Location Map Viewer I use with the gpx files I get from GPS logger to visualize my movements.
• mpv just plays a lot of media without being a bloated thing like vlc. I use mpv for videos, vlc for music.
• NewPipeSponsorblock is available in a custom repo only.
• Ning is a nice way to get an overview over a local network.
• OpenTracks can be used in combination with GadgetBridge to record your sports with gps.
• OSMand gives you a frontend for using openstreetmap with offline maps, navigation and more.
• PDF Doc Scan is my way to digitalize important letters as a pdf on the go.
• StreetComplete is a gamificated way to fill in missing things in openstreetmap. it’s fun.
• Syncthing-Fork (important to use the fork) is a file sync tool I use to backup a lot of my phones folders to a pc.
• Tusky is my favorite way to browse mastodon.
• VLC is a powerful media player (I then use only to shuffle through my mp3s).

This is such a great list, saving and installing a few!

Adding on (and likely seconding a few):

• 2048: game
• Aegis: for 2Fa stuff
• AntennaPod: second this one
• AnkiDroid: Flashcards, the Anki project is huge and extends way past android. Worth exploring if you want/need to memorize things
• Droid-ify: Fdroid client I use, but I keep the main app installed too
• Eat Poop You Cat: game to be played in a group
• Feeder: for RSS
• FFShare: for compressing photos/videos before sharing
• FlorisBoard: The keybaord I liked, although I don’t use it full time
• GPTAssist: Frontend for chatGPT
• Material Files: File manager
• Native Alpha: Have websites run like apps, while isolating each site
• OpenFoodFacts: A bit buggy, but it’s similar to OSM but for food
• RetroStack: Another game
• SDMaid SE: Same dev from the popular playstore one, is rebuilding a better one from scratch, AND it’s now FOSS
• SkyMap:
• Survival manual
• Termux
• Translate You
• UntrackMe: To redirect Tiktok/Twitter/Pinterest/etc. links to the frontends
• URLCheck: Highly recommend getting this one to clean trackers from links
• Unitto: Calculator of choice. I explored a bunch before settling on this one

For OSM specifically, I second the ones mentioned. Here are some other OSM related things: lemmy.ca/post/6586265