This is known as a Knapp joint (for the inventor) or a “pin and cove” (descriptive name).
It’s a distinctive appearance, and has the advantage of not requiring special tooling, but it does require a vertical fixture such as:
and then at minimum 3 operations:
- cut parts to length/size and machine interior features (rabbet for a bottom/lid, &c.)
- mount all four boards on the machine and cut the joint for two corners
- repeat for the other corner
If you don’t set up the file for cutting two corners at a time, it’s 5 operations.
An alternative is to use joinery designs which allow cutting the parts flat on the table — for the photo for the box below, no glue was used:
See:
and
I’m working on a simpler version which will allow test fitting first, and won’t require the narrow V endmill: