dupeGuru

dupeGuru is a free and open source tool to find duplicate files on your computer. It can scan either filenames or contents. The filename scan features a fuzzy matching algorithm that can find duplicate filenames even when they are not exactly the same. dupeGuru runs on Mac OS X and Linux. Windows used to be supported, but it's not anymore. Last version, 3.9.3, can be still downloaded from the official website and it works on Windows 7.