hardlink

hardlink is a tool which replaces multiple copies of a file with hardlinks.
Inspiration came from http://code.google.com/p/hardlinkpy/, but no code has
been used.

This version was originally written in Python as well, but performance issues
on large data sets caused it to be rewritten in C.

Source: https://salsa.debian.org/jak/hardlink

This is also available in util-linux verion 2.37 (2.34 ships *a* hardlink, but not *this* hardlink).