Update: added "mouse ears" to the naef to doblo adapters, to help them stay flat when printing. Also added the 2x2 adapter.

For the doblo to naef adapter, just print it. You can use 3x3 or 4x4 nibbles size.

For the naef to doblo adapter, print the bottom part first (this is basically a half block). Then print the appropriate top, either 3x3 or 4x4 nibbles. Glue the top and bottom together, using bits of filament in the registration holes to keep everything aligned.

You can edit the OpenSCAD file to change the radius of the registration holes, make bricks with a custom number of nibbles, or even make them Lego compatible! You can also change the height of the fillet that adapts between the doblo and naef block, it is the variable dim_f.