Sorted them into a few categories

Social

• Cheogram - xmpp chat, can also handle phone and sms gateways

• Fedilab - my preferred fediverse app for mastodon

• Jerboa - preferred lemmy app

• K-9 Mail - email

• Pixelix - pixelfed app. not sure if I like this or PixelDroid better yet

Media

• AntennaPod - podcasts

• Kiwix - offline copies of useful wikis, q&as, archives, etc.

• Librera FD - books

• NewPipe - watch youtube videos, although google keeps trying to break it

• Voice - audiobooks

Security

• Aegis - two factor authentication

• KeePassDX - password management

• WG Tunnel - VPN connection, still not sure if this is the best option

Notes and Documents

• Orgzly Revised - note taking. for people not familiar with emacs something like logseq or safe notes might be better

• Pinkt - bookmarks

• Syncthing-Fork - synchronize files between devices

System

• F-Droid - technically it can install itself

• Lawnchair - alternative home screen / app launcher

• ntfy - runs in the background, handles push notifications for some other apps

• Unexpected Keyboard - has the fancy keys that most android keyboards leave out

Other Tools

• Fennec - basically firefox

• Organic Maps - sometimes missing info and it doesn't have traffic data. simpler than OsmAnd

• PocketPaint - make art on your phone

• QuickDict - offline multi-language dictionary

I've got hundreds more installed, but those are some of my favorites.

Organic maps

• Aegis
• Audire
• Binary Eye
• DavX5
• Droidify
• Image Toolbox
• Immich
• KDE Connect
• LibreOffice Viewer
• Muzei
• NextCloud
• Paperless Mobile

• FlorisBoard
• URLCheck
• AdAway
• AppManager
• LocalSend
• Syncthing-fork
• DataBackup
• SD Maid
• Track & Graph
• Simple Time Tracker
• OpenTracks
• OrganicMaps
• YTDLnis
• Aegis
• Aves
• Image Toolbox
• Read You
• URL Radio

I'd like to add Broccoli as a database for cooking recipes. It is very convenient, as it extracts the relevant data out of most SEO-inflated webpages.

fossify gallery is pretty nice

Others here have already mentioned most of the ones I use.

Some that are less common are

• The Fossify suite of apps
• Eternity for Lemmy browsing
• Spotube for music streaming
• OsmAnd for navigation
• Converter NOW for conversions

The most useful one though is probably Syncthing. It lets you synchronise folders between your devices.

Pipepipe - newpipe fork with sponsorblock and Google account fallback for restricted videos

Quillpad - Google Keep replacement

KeepassDX - password manager and nice keyboard that autotypes what you want without copy pasting

Syncthing-fork - for syncing files

• Termux (or equivalent) has always been the primary mobile phone use case for me. Access to my main computing platforms from my pocket.
• Antennapod
• Fedilab (Mastodon)
• Fennec - Can't deal with the web without uBo and other extensions.

• Kvaesitso - my favorite launcher
• Material Files
• Fossify camera
• Fossify gallery

• KDE Connect
• IronFox: fork/successor to the defunct Mull browser
• OSMAnd~
• AntennaPod
• Transistor: for internet radio
• Any music app, they're all good; I'm currently using Symphony
• Jerboa: for Lemmy

• Fennec

• Eternity

• Newpipe

• Clima

• Organic Maps

• Fossify Notes

• Barcode Scanner

• Vernet (network scanner)

A few I've not seen mentioned yet:

• Equate - calculator/converter etc
• Feeder - RSS client
• Immich - Photos. App for self hostable server
• Jellyfin - media client
• Joplin - notes
• MJ PDF - PDF viewer with extras
• PDF Converter - handy PDF tool
• Squawker - view the cesspit, follow stuff etc
• Subz - track your subscriptions
• Untracker - removes tracking info before sharing links
• Whobird - Shazam for birds

• QuillPad
• AntennaPod
• NewPipe
• Aegis
• RetroMusic
• Organic Maps with Sherpa Onnx voice
• OSMAnd
• FUTO Keyboard
• Signal/Molly

Expand this from F-Droid to Obtainium 😉