The recent paper on the aperiodic monotile by Smith, Myers, Kapman and Goodman-Strauss discusses “The Hat” monotile with a delightfully simple geometry. It is very easy to construct in a parametric Cad program, for people interested here is a version in the FeeCAD.

The 2d geometry with the constraints, illustrating the construction using three hexagons and perpendicular bisectors is shown below: Construction

A 3d Rendering:

3d Rendering

FreeCad source