Moriyama UDiff allows you to compare an Umbraco webroot to an Umbraco release zip and extract the differences.
It can be used for the following purposes:
Scheduled task on a production server to backup changes on a regular interval
Extract customisations from an Umbraco site that you have inherited (that isn't currently version controlled)
A post build event in your visual solution to copy changes to a source controlled directory (ideal for Team development)
Peforming upgrades - UDiff can tell you which files you need to copy into a clean version of Umbraco