One more possibility.
The boards are not rectangles.
They are triangles with the base to the left and the
points to the right.

Art

"Wood Butcher" wrote in message
...
312. Assuming no glue, some sort of fastner was used ...

The center of gravity of all the boards above the top
right corner of any individual board is to the left of that
point.

Also plausible:
An interlocking joint was used.

It is a trick photo and the table is not level, the right side
is higher than the left. Or the camera is looking down
on the stack.

There is airflow from the right which provides pressure
to hold the stack up.

Art

"R.H." wrote in message
snip
312. There is more overhang in this stack of wood than you could
normally get, though with nothing to compare it to I guess it's hard to
tell. I'd like to change the question here to: What design feature was
used to maximize the horizontal overhang?