Steve Ramsey of Woodworking for Mere Mortals did a great video on french cleats recently.

Steve's video  is what started me on this quest.  Thanks everyone  for your help.

Hi Gary,

Here are a variety of photos/images, of French Cleats in use.

The French Cleat, concept has been around for many years.

Where did it originate? 

Don't know for sure---nothing archived in history.

However, in the early 17th century, houses build in France, were mainly constructed of earthen materials.

The walls were not strong enough to hang heavy wooden objects; 

therefore, cleats, a simple object, were fashioned from wood and affixed to the walls, to hang heavy wooded objects.

I recall seeing my granddad, having his horses harness, neck collar, and the like, hanging on cleated wood pegs.  The peg was affixed to a block, that hooked on the cleat---and adjustable from side to side,

so as to accommodate various size objects.

He also had many of such fashioned items in his workshop and other buildings.

A peg into a block, was a commonly used item.

In many instances, it was more useful over putting a spike, nail or peg on a wall or in a post.

Put pegs, or the like, in a block and hang up your yard or garden tools.

(Attach 1x stock on a wall, with the 45 degree chamfer on the back side, and hang the cleated block).