NoDoubles

NoDouble is a duplicate correction tool. It scans your drives for duplicate file. Unlike most tools, it replaces duplicates with hard links.
A duplicate file is file with the same content, the same size, but not necessarily the same name or extension.
When two duplicates or more are found, at least one of them is replaced with a hard link that points to the same data in the first file. Effectively, a hard link is a file, not a shortcut, and by removing the first file, the second file will still be present with all of its data. However, modifying one of these files leads to the modification of the other.