CodePanic's FileMany is a free tool that scans your hard drives for duplicate files, which you can then choose to move, delete, or ignore. It uses a variety of customizable criteria to distinguish actual duplicates from merely similar data to help you avoid the regrettable error of deleting the wrong files. Even if duplicate files aren't a big issue, running FileMany before you clean or defragment your drives can make the process faster and help reduce errors. And if you boot from an SSD, especially a smaller one, FileMany can help you keep your free space free and prevent your drive from filling up and slowing down.
FileMany's installer offers two interface language options, English and Japanese. FileMany's user interface is a simple but stylish take on the standard Explorer layout: toolbar, sidebar with tree view, and a tabbed main window. FileMany's sidebar not only has the obligatory (and welcome) tree view for navigation but also an Image Preview tool, something else that is absolutely essential in a duplicate finder. The main window's tabs access Files, Folders, a Log, and duplicated files and folders, with the ability to search, clear, or delete files as needed. You'll want to have a look at the program's General Search Project Settings, which include the ability to specify search method. The default choice is hash, with a submenu for specifying the hash algorithm, but we could also search by file name, size, and binary as well as text. FileMany has quite a few other options for searching and excluding files, including by filename, extension, or attribute.
We ran a basic search on our main hard drive as well as a USB drive with backup directories. FileMany identified many duplicates, which we could delete or clear as needed. We saw no misidentified duplicates, either. And we like the ability to save searches as projects to run regularly. Some of the program's labels didn't translate from Japanese to English, and the Help file linked to a Wiki in Japanese, which could cause some confusion. If so, try one of the many similar freeware duplicate finders available.