bsdiff (Binary diff/patch utility)

bsdiff and bspatch are tools for building and applying patches 
to binary files. By using suffix sorting (specifically, 
Larsson and Sadakane's qsufsort) and taking advantage of how 
executable files change, bsdiff routinely produces binary patches 
50-80% smaller than those produced by Xdelta, and 15% smaller 
than those produced by .RTPatch (a $2750/seat commercial patch tool).

Website: http://www.daemonology.net/bsdiff/
License: BSD-like
Author: Colin Percival <cperciva@freebsd.org>
