A while back I found this in a huge and famous german hardware store chain (Bauhaus):
It is this (intro vid)
And it is actual open hardware!
When I browsed through the website of Playwood IT could not find the 3D printable file for download only other materials.
But when I sent them an email they were happy to share the file and it took @nikusha not long to find the file on instructables as well.
Design Files (by intructable user: exilaus; license: cc-by-sa)
wood_connector_for_finiture.zip (948.2 KB)
I think this design is quite interesting for circularity:
(1) it does not harm the material you use with it - no drilling etc.
(2) you could actually try and use it with old wood and be quite flexible.
As often. It is not a 100 percent circularity solution. But … on its way.