Aqil Raharjo, a design student at the Ontario College of Art and Design in Toronto, calls his invention the Schnap. With it, you can take a nap in a snap (hence the name).
You can rig just about any hammock for this purpose. But the Schnap makes workplace slacking easy. It's held in place with 2 c-clamps, which are mounted on wood table protectors to prevent marring by the clamp feet.
Not only is the Schnap quick, it's also descreet. If fits under a desk, thus making it less likely that your supervisor will notice you. She'll just think that you're away from your desk.