To put it crudely, it's basically a sock with the sole of a running shoe attached to the bottom of it.
It retails for $160, and goes on sale August 1st.
Nike has been trying to make running shoes that mimic what it's like to run barefoot ("naturally") for a while. The current Nike Free has a flexible sole that curves to the motion of your foot as it hits the ground, and the support on the upper parts of the shoe is less bulky than traditional running shoes.
The sole of this new Nike Free Flyknit is the same as the Nike Free, but the upper is a knitted material that's really sock-like.
It seems pretty wild, but we're guessing it might be a little too extreme for non-hardcore runners who don't want to drop $160 on a shoe they've never experiences before.
The shoe:
The top of the upper is a sock, but there's slightly more support at the heel to keep your foot in place:
The sole:
A close-up of the fibers:
The eyelets: