Create MD5 checksums for single files, or whole groups of files. MD5 Ceckfrog can make one checksum file that includes all the files in a folder, and even subfolders, or select the folder and have it make individual md5 files for every file.
Hard drive getting full? Afraid you may have a lot of duplicate files, but don't know where they all are? Duplicate Finder will search for files that have the same content, even if they have different filenames.