The standard file formats do not support the kind of advanced features that Obnam is built for. For example, block level de-duplication, or abolishing the difference between full and incremental generations. It would be possible to build those features on top, say, tar, but it would mean the tar is just a container for odd bits of data, which still requires a custom program to restore from.

If you're worried that you might lose your copy of Obnam, and be unable to restore, two points:

• You can store a copy of Obnam (in source and binary versions) in your backup repository.
• Obnam is free software, and it's in Debian. You're pretty much guaranteed to be able to find a copy and build a new binary.