Skylab Shoe

Sections of Skylab's flooring were composed of a triangular grid and the astronauts' shoes had a triangular cleat which would protrude through the floor and twist to lock. Once properly anchored, the astronaut could then exert force on objects without that pesky "equal but opposite reaction" from hindering him.

Refer to Skylab, Our First Space Station for information and a photo of the Skylab shoe and grid system. Also see the Smithsonian's page on a pair of flight shoes (scroll down to the tenth photo for a view of the bottom of the shoe).

Here's a picture of the flooring in one part of Skylab, showing the grid system.