most photos courtesy of Ed Tyanich
The Runner's Harness is a very specialized item. It is for folks wanting to put together a dedicated running vest comprised of a Kit Bag on the front and a backpack on the back. To use the Runner's Harness, you start with any model of Kit Bag (sold separately) and remove the H-harness from it. Then you take a Tarahumara or Umlindi (sold separately) and remove the shoulder harness from the pack. The Runner's Harness then ties the naked Kit Bag and naked Backpack together into a single vest. In the process of doing this, you lose the ability to use either of the two items separately without re-rigging them. However, if you're a dedicated trail runner (like these guys) who wants to be adequately prepared for the elements, this might just be the setup for you.
Check out the dedicated forum thread for more information including setup.