Inspired by the Hex Connectors from TonyH0612, but redesigned for my needs.
Fits 1/8 inch boards, with holes for #6 1/4 inch wood screws. The "b" versions have a hole so they can be attached to the wall as well, for mine, I used some drywall anchors.
I added a V2, that no longer expects screws, instead, a drop of glue should hold things tightly. It also puts a little bit of plastic between the different pieces, so they fit very nicely with no give.