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