Kosmotheka

Kosmotheka catalogues what a household owns (books, comics, board games,
films, video games, music) and where each thing is, and shares that
catalogue with the people you live with.

It is local-first: it works fully offline and without an account, keeps
your data on your devices, and syncs paired devices directly over your
home network. An optional account keeps a library in sync from anywhere
and lets you invite other people; you can also run your own server.