bsdiff: http://www.daemonology.net/bsdiff/
Courgette: http://www.chromium.org/developers/design-documents/software-updates-courgette
http://blog.chromium.org/2009/07/smaller-is-faster-and-safer-too.html
xdelta: http://code.google.com/p/xdelta/
rdiff: http://librsync.sourcefrog.net/