SyncThing - to sync my files between devices and avoid the big corporations cloud (use it for notes, Keepass database, photos, etc)
Logseq - super advanced note taking with tagging and relationships between notes (all store locally)
Authpass - opening my Keepass password database on my phone
GrapheneOS Camera - just to avoid the Google camera app as I have Google Photos disabled on my phone and needrd a good app that doesn't break when going to view the gallery (since it tries to open Google Photos)
Simple Gallery - to view my photos on my phone
Signal - I have it but I have very few friends that use it unfortunately
AntennaPod - for podcasts, I'm thinking of self hosting a podcast tracker to sync my listening habits across my devices, we'll see if that happens
Vinyl Music Player - to play my local mp3 files and playlists (I use MusicBee to manage what I sync to the phone as my mp3 library is quite large, and SyncThing to actually copy stuff over)
I guess it depends how old we were when these things came out. I missed out on the sharing videos from flash sites and really got on the internet and using it regularly when youtube was already a thing.
Personally for me, I don't want to store my personal files in anybody else's cloud besides mine. I don't want Google to have them, I don't want Apple to have them. I use Syncthing to sync files between my devices. My understanding is it is a much better implementation on Android than Apple (basically non existent due to rules for apps on iOS is my understanding)
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