Delsum is a reverse engineering tool for checksums.
It can do a few things (changable in the "Options" section):
Reverse: You can add some files and their checksums under the "Files" sections, and delsum will attempt to find all checksum algorithms that fit the patterns specified under the "Models" tab.
Part: You can add some files and for each a checksum under the "Files" section, and some checksum algorithms under the "Models" section and get all common file ranges for the files that have the respective checksum.
Checksum: You can get a table that just gives the checksum for each file and checksum algorithm combination.
A more thorough explanation is available in the project README.