A braiding fork or knitting fork also called a lucet is used for making cords. The tool and technique date from the Middle Ages and was used by the Vikings for making rope.
These cords consist of a series of loops that could be considered knotted. This creates a very sturdy elastic square cord that does not fully unravel when a thread snaps.
There is no limit to the length so you can have lots of fun making very long strong cords.
Note: Yarn not included.