A diff utility which works with binary files

 Xdelta is an application program designed to compute changes between
 files. These changes (deltas) are similar to the output of the
 "diff" program in that they may be used to store and transmit only the
 changes between files. However, unlike diff, the output of Xdelta is
 not expressed in a human-readable format--Xdelta can also apply
 these deltas to a copy of the original file. Xdelta uses a fast,
 linear algorithm and performs well on both binary and text files.