Keepass and its various forks are open source. Keepass itself uses dotNet so Linux guys need mono which not all people like. Those people use KeepassXC (a fork of KeepassX which is Keepass in C++ and is unmaintained).
I use Keepass. Reasonable security but ugly gui in linux due to mono. Has plugins. Completely offline.
I use Keepass. Reasonable security but ugly gui in linux due to mono. Has plugins. Completely offline.