I had the idea for a continuous calendar based on a split flap style clock.  The calendar may be 100% 3d printed, or 2x ¼-20 screws may be used to hold it together.  

This calendar is manually operated by turning the dial on either side toward you to rotate through the month and date.  I have included the step file for the removable face plate so you can customize it if you wish.

Printed from PLA, 0.4mm nozzle 0.2 layer height except the flappers.  Flappers are printed 0.08 layer height with a pause to change filaments to get the dual tone styling.  Some sanding/trimming may be required to fit smaller pieces together depending on printer tolerances.