These brackets form a four-way junction, a T junction, and corner junctions at the feet, for 1" square pieces of wood. As you'll see in the pictures, I made them for a specific purpose related to container gardening, though you may find other uses for them.
The container garden growing tomatoes needs something to tie the tomatoes to, and those inverted metal cones don't work well in container gardens (well, they don't work well at all, but especially there), so I built a simple frame. To keep costs down I used 1"-square gardening stakes, and simply cut them to make crossbeams. The result is effective but it can be a bit wobbly and rickety, especially when being moved, because of the corners held together only with nails. Because the wood's not strong enough for a very long wood screw.
I considered lining the corners with L-brackets but that seemed expensive. So I designed these brackets which join vertical and horizontals, either one or two horizontals at the same point, plus two for the feet (designed to have no plastic at the bottom).
I put in way more screw-holes than you really need, to make it easier to place ones wherever there isn't a nail in the way, and still have enough to hold sturdily.
The pictures show the whole container garden, the join without the bracket, and the join with the bracket, before and after wood-screws.