This is an iris mechanism built into a business card sized card.
The design files can be downloaded here: http://www.thingiverse.com/thing:8787
Another version with 4 leafs: http://www.thingiverse.com/thing:8944
The paper needs to be fairly thick because it needs some stiffness to operate. I use a 14 point (0.014") paper
It can be cut by hand, but it would of course be much easier on a laser or paper cutting machine.
bburke37 made it!