I've developed in my (scarce) spare time this Linux library to decrypt 1Password databases in OPVault format:
This is alpha quality software: it's pretty untested and lacks of a lot of features, but I can decrypt successfully the (2) sample databases I have.
If you can help to complete the library, get in touch!
If you have front end dev skills, feel free to use the library to create a proper GUI app. In the test directory there is a straightforward usage example (no docs yet ).