What is a hexaflexagon you might ask. The animated gif to the left gives you the general idea.
A really awesome intro video that is a must watch for hexaflexagon enthusiasts was made by Vi Hart.
More info on Wikepedia.
This is a tool to create hexaflexagon templates with your own artwork like these:
Use the sketch tool create your artworks.
Create one to use as an edge piece. An image that has mirror and a multiple of 3 rotations work best.
Select the images from the Galery to use for an edge and for faces.
Print out the template by either:
Clicking the print button which opens another tab and the print dialog.
Right clicking the template and saving it for later printing.