This model is based on Zack Freedman's Gridfinity and Kyle Warren's screw together adaption. My version uses a dovetail connection to connect individual modules into any configuration.  The connection is tight and requires a tool to gently tap the connection together.  A step file is included for modification and adaptation.  No support is required, however, I use support in the dovetail voids and they pop right out.  Accommodation for 6x2mm magnets is on top and it doubles as a counterbore for #4 screws.

Added an all void version by request.

Shorter version with symmetric dovetails here.