btar is a tar-compatible archiver which allows arbitrary compression and ciphering, redundancy, differential backup, indexed extraction, multicore compression, input and output serialisation, and tolerance to partial archive errors.
The original btar program is created and owned by Lluís Batlle i Rossell, and licensed under the GPLv3 (which you can find in ./LICENSE, as well as the original tarball). I'm just a mediocre script kiddie who's trying to make a version of btar that I can submit to the FreeBSD ports tree. (with the author's permission, of course.)