http://xdelta.org/
http://sourceforge.net/projects/xdelta/
http://downloads.sourceforge.net/xdelta/xdelta-1.1.3.tar.gz
http://downloads.sourceforge.net/xdelta/xdfs.pdf
http://downloads.sourceforge.net/xdelta/xproxy.pdf

# historic
http://www.xcf.berkeley.edu/~jmacd/xdelta.html