Nålbinding is a yarn craft that pre-dates knitting and crochet. It is mostly associated with Scandinavia, dating back to the Viking era. Examples being found during archealogical investigations. But has been found in many other areas around the world. 
It involves the use of short lengths of wool being knotted together to form a fabric, using a single short needle. As more yarn is needed to extend the work, new lengths are felted together. 
Different knots produce different textures and designs and are often named after the place where examples were first found. E.g.:  York stitch or Oslo stitch. 

Because it involves a knotting system, the result is a fabric that doesn't unravel. Often used to make hats, mittens or scarves, but can be adapted in all sorts of ways depending on the skill of the maker. 

I was attracted to it for a few reasons. Firstly because of the use of wool only; secondly, because I could whittle my own needles; and thirdly; because of my Scandinavian heritage. It just fitted. 

I am by no means an expert, but i feel competant enough to pass on the basics to get someone else started.