Passwordstore¹. A single, simple back-end specification — a file and folder hierarchy where each plain text file is encrypted using GnuPG — and a number of clients for any common platform.

If you want to keep it simple, just use the command-line `pass` utility. You can verify the workings of that fairly simple script yourself.

If you want to share your database across multiple machines, you can use git, or a non-cloud synchronisation tool such as Synthing². You can even encrypt (parts of) your password tree for multiple recipients (all using OpenPGP key-pairs).

Personally, I really like the setup I have with Syncthing and `pass`.

1: https://www.passwordstore.org/

2: https://syncthing.net/