I happened upon an intriguing utility this morning by way of
Open Source Digital Forensics (which I discovered on one of Bruce Schneier's
blog entries):
ssdeep : "Recursive computing and matching of Context Triggered Piecewise Hashing (aka Fuzzy Hashing). Supports Windows, *nix, BSD, OS X, etc."
The main interest area to me is its "
matching mode", which uses so-called fuzzy hashing to produce a weighted score, indicating the extent of the match.
(BTW, I found one brief mention of this utility on LQ
here, but decided to give it its own honorary thread.)