Quilt is a set of scripts to manage a
series of patches by keeping track of the changes
each patch makes. Patches can be applied,
un-applied, refreshed, etc. The key philosophical
concept is that your primary output is patches,
not ".c" files or ".h" files, so patches are the
first-class object here. It was originally based
on Andrew Morton's patch scripts published on the
Linux kernel mailing list a while ago, but has
been heavily modified since then.