So far the software is not available, since it's not working well enough that ordinary people could help with it. When we release it, it will be free software, under the GNU General Public License.
Grokmail maintains a database separate from your email, but synchronized with it. Hooks for the MH mail handling system, and the MH-E emacs interface to it, are being built. It's designed to be pluggable into any email reader, eventually.