Name: Buttercup
Homepage: https://buttercup.pw/

Why? --> It's just great and easy to use. I think that for average newbie user it's much easier to use than keepass or gopass.

Is it open source? --> Yes

Github: https://github.com/buttercup/buttercup-desktop
Github releases page: https://github.com/buttercup/buttercup-desktop/releases
There is an AppImage file

Latest tarball link https://github.com/buttercup/buttercup-desktop/archive/v1.19.0.tar.gz