Can Alice and Bob share repository without sharing file data?

This doesn't work particularly well. Obnam does not currently support it at all. On a conceptual level, it could work, by turning all de-duplication off, and having Alice and Bob encrypt their own chunks only with their own, separate keys.

However, it would be simpler to just have a separate repository for each of them. That would also prevent either of them to remove the other's files.

What does the name "Obnam" mean?

Back in 2006, when Obnam started, we wanted to have a name that was short, reasonably pronounceable by major cultures, and did not have too many Google hits. After much trying, we failed to come up with anything good. However, without a name, you can't even start the project, because what will you call its source directory? So we chose the OBligatory NAMe.

How do I restore on another computer?

Use --client-name and set it to the name of the computer that made the original backup.