dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.
VisiPics - VisiPics does more than just look for identical files, it goes beyond checksums to look for similar...
Rdfind - Rdfind is a program that finds duplicate files.
FSlint - FSlint is a utility to find and clean various forms of lint on a filesystem. I.E.
Pixiple - Find images similar in pixel and/or metadata content
AllDup - AllDup is a freeware tool for searching and removing file duplicates on your Windows computer.