This is GNU Stow, a program for managing the installation of software
packages, keeping them separate (/usr/local/stow/emacs
vs. /usr/local/stow/perl, for example) while making them appear to be
installed in the same place (/usr/local).

Stow was inspired by Carnegie Mellon's "Depot" program, but is
substantially simpler.  Whereas Depot requires database files to keep
things in sync, Stow stores no extra state between runs, so there's
no danger (as there is in Depot) of mangling directories when file
hierarchies don't match the database.  Also unlike Depot, Stow will
never delete any files, directories, or links that appear in a Stow
directory (e.g., /usr/local/stow/emacs), so it's always possible to
rebuild the target tree (e.g., /usr/local).