KDEConnect - I use it on Windows and android phone. Very nice when you get security codes or links on phone, want to send files or when I want to control audio|video and I watch from the couch.
in general: Fdroid nearly always has a more feature rich and performant alternative
Immich. Just found out about it, still gotta try, but looks good, an app that allows you to configure a Google Photos like app locally hosted, with automatic phone backups
Paperless-ngx that allows you to self host an easily browseable archive of your documents. Fully featured with OCR, ML-powered categorization and the works.
I personally would recommend it over Bitwarden since with Bitwarden you NEED internet to access your passwords, and even if is open source, i canmot trust it, security breaches can happen in any time, having your vault locally stored helps a lot.
There are more but i can't Remember them right now.
I just tried because you made me doubt, but you can access your passwords offline with bitwarden. Your argument about trusting a third party is far more pertinent, i'm choosing to trust them but thats really my choice. It is also a limited trust: even in a case of a data breach, bitwarden is encrypted end-to-end with your password, even if someone gets access to your data they wont be able to read it without your master key.
Another thing like that I wish I'd discover sooner is syncthing - it's really intuitive, just point it to a folder and it syncs stuff across your devices automatically. With it, a lot of cloud storage, backup and file transfer applications and features are completely redundant.
EDIT: Ah, I did not scroll far enough to see that this recommendation is literally the next comment from this.