F-Droid

• Aegis - two factor authentication

• AntennaPod - podcasts

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

• F-Droid - technically it can install itself

• Fedilab - my prefered fediverse app for mastodon

• Fennec - basically firefox

• Jerboa - preferred lemmy app

• K-9 Mail - email

• KeePassDX - password management

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

• Lawnchair - alternative home screen / app launcher

• Librera FD - books

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

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

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

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

• Pinkt - bookmarks

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

• PocketPaint - make art on your phone

• QuickDict - offline multi-language dictionary

• Syncthing-Fork - syncronize files between devices

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

• Voice - audiobooks

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

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