pax - Portable Archive eXchange
Bu requires pax as of version 3.4 beta.
Pax is part of the base system on BSD.
Most major Linux distributions should come with pax or have a pax package available. However, I make the source available here in case yours doesn't, or in case you want the source code of a Linux port.
This was ported to Linux from OpenBSD and is maintained by SUSE Linux. It came from http://ftp.suse.com/pub/people/kukuk/pax/
Pax is the BSD drop in replacement for tar and cpio, only it is more robust. It is command line compatible with both when run as the same name and it has it's own command line interface when run as pax. It's own native command usage provides the stream like functionality of cpio but is more simple and convenient to use interactively like tar.
See the bu Changlog for a detailed explanation of why I chose pax rather than staying with GNU tar or cpio.