Andrew Morton originally developed a set of scripts for maintaining
kernel patches outside of any SCM tool. Others extended these into a
suite called quilt. The basic idea behind quilt is to maintain patches
instead of maintaining source files. Patches can be added, removed or
reordered, and they can be refreshed as you fix bugs or update to a new
base revision. quilt is very powerful, but it is not integrated with
the underlying SCM tools. This makes it difficult to visualize your
changes.

Guilt allows one to use quilt functionality on top of a Git repository.
Changes are maintained as patches which are committed into Git.
Commits can be removed or reordered, and the underlying patch can be
refreshed based on changes made in the working directory. The patch
directory can also be placed under revision control, so you can have a
separate history of changes made to your patches.