Arch is a really nifty revision control system.  It's "whole-tree changeset
based" which means, roughly, that it can handle (with atomic commits) file
and directory adds, deletes, and renames cleanly, and that it does branching
simply and easily.  Arch is also "distributed" which means, for example that
you can make arch branches of your own from remote projects, even if you do
not have write access to the revision control archives for those projects.

WWW: http://www.gnu.org/software/gnu-arch/