Need to get my Keepass database on my phone? Syncthing.
Need to back up my reMarkable to my NAS? Syncthing.
Need to replicate game saves between my PC and my Steamdeck because the game doesn't support Steam Cloud Sync (I'm looking at you, Subnautica)? Syncthing.
I run Paperless as a document management system and use Genius Scan on my phone. I use Syncthing to automatically move scans from my phone to the Paperless inbox folder.
And none of that data resides on a third party cloud. Just encrypted, peer-to-peer sync. It really is fantastic.
https://docs.paperless-ngx.com/
Think: replacing paper file folders with a digital system. Supports OCR, a variety of metadata, tagging and categories, etc.
My primary use case is taxes, but for any important legal or financial documents, I throw 'em in Paperless.
Does it run on those?