KeePassXC ( https://keepassxc.org/ ) - open source, full featured, standard file format, bring your own cloud storage
Similarly to this API compatibility there's KeePassDX [2] for mobile phones which is compatible with the KeePass database format. There's also KeePass [3] which is the original built with .NET.
I personally use Bitwarden though because maintaining sync of databases on mobile phones is painful. Also keeping backups up to date is hard and time consuming, I do export my encrypted database once in a while though.
[0]: https://www.passwordstore.org/