Aurora Store - Anonymized frontend for Playstore
F-Droid - Open Source App Store
Obtainium - App Store for other sources (e.g. github)
Organic Maps - Open Source navigation (not as good as proprietary ones though)
SherpaTTS - Text to speech for Organic Maps
PDF Doc Scanner - Little Trickster, Open Source document scanner
Binary Eye - Barcode reader
K9 Mail / FairMail - Mail client
LocalSend - Cross Platform File Transfer
Syncthing Fork - Catfriend1 Syncthing fork to sync files
VLC Media Player - media player
KOReader - ebook reader
Voice - Paul Woitaschek, local audiobook player
AudioBookShelf - Remote audiobook player
Immich - image backup
Fossify File Manager - file manager
Substreamer / DSub - Audio streamer for navidrome self hosted server
OpenCamera - Open Source camera app
I wish I had this list from the start... Hope it helps someone :-)Note that a community fork done by some core contributors was just spawned: CoMaps [1]
> K9 Mail / FairMail - Mail client
And now there's Thunderbird, which is branded version of K9 Mail IIUC (I don't know if there's any reason to switch from K9 Mail to Thunderbird for existing users)