First launched in 2006, the Nike Free was the first running shoe that was meant to be used as a training tool, to be added to your rotation of running shoes.
Featuring extremely deconstructed upper and soles - they tried and recreate the feeling of running barefoot with the aim of strengthening the muscles in your feet. Originally identified by a number (3.0 5.0 or 7.0), they are now offered in a great variety of materials and flexibility. You can see all the other Nike Running Shoes here.