Free-Sole socks are socks that are knit in such a way that all or any part of the sole can be cut off and reknit (easily) should holes happen. This sock architecture was thought up by the Brilliant Anna Zilboorg.
The start is a small piece of stockinette, just a few stitches wide (4 in this case) with live stitches at either end. A marker is place in the exact center.
To start the instep, you pick up an equal number of stitches on either side of the center.
Then you begin knitting, picking up stitches at the end of each row - so you pick up one on each side every two rows.
When you get to the end of the little piece of knitting, you have finished the toe. That's when you pickup the live stitches at the ends of the starting piece.
Then you knit flat until the instep measures 2" less than the length of your foot.
Now it's time to start on the sole. You pick up the same number of stitches on either side of your center marker. Since you are picking up stitches and these are not live stitches, should holes arise later, you can simply cut this part off the sock and re-knit the sole.
Once again, you knit picking up stitches on either end until you have increased enough for your toe.
Once the toe is complete, you pick up the stitches on the sides, but knit them together with the last stitch from the previous row. That way you are still attaching the sides but not increasing anymore.
This is what it looks like when someone tries on the sock in progress.
Once you have knit to a certain point, you go back to increasing for a gusset.
Then turn the heel with short rows.
Then we knit the heel flap and decrease the gussets on each side.
And finally start up the leg just like any other toe up sock.
I think it's brilliant and it's certainly not difficult to knit!
Knitting Socks from Around the World has the Poppy Sock which is free-sole.
Magnificent Mittens and Socks has several free-sole sock patterns.
Socks for Sandals and Clogs has free-sole sock patterns.
Free-Sole DVD has the Half Stranded Sock pattern and has Anna explaining, step by step how to knit these socks.