Sorted them into a few categories
Social
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Cheogram - xmpp chat, can also handle phone and sms gateways
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Fedilab - my preferred fediverse app for mastodon
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Jerboa - preferred lemmy app
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K-9 Mail - email
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Pixelix - pixelfed app. not sure if I like this or PixelDroid better yet
Media
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AntennaPod - podcasts
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Kiwix - offline copies of useful wikis, q&as, archives, etc.
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Librera FD - books
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NewPipe - watch youtube videos, although google keeps trying to break it
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Voice - audiobooks
Security
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Aegis - two factor authentication
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KeePassDX - password management
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WG Tunnel - VPN connection, still not sure if this is the best option
Notes and Documents
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Orgzly Revised - note taking. for people not familiar with emacs something like logseq or safe notes might be better
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Pinkt - bookmarks
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Syncthing-Fork - synchronize files between devices
System
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F-Droid - technically it can install itself
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Lawnchair - alternative home screen / app launcher
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ntfy - runs in the background, handles push notifications for some other apps
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Unexpected Keyboard - has the fancy keys that most android keyboards leave out
Other Tools
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Fennec - basically firefox
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Organic Maps - sometimes missing info and it doesn't have traffic data. simpler than OsmAnd
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PocketPaint - make art on your phone
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QuickDict - offline multi-language dictionary
I've got hundreds more installed, but those are some of my favorites.