Single cask whiskies are one-offs, they will never be repeated with each cask only producing a limited amount of bottles. Every cask of whisky has had its own interaction between wood and spirit, each one creating an entirely unique arrangement of flavour and character. Usually single casks are bottled at cask strength but some are controlled to a more approachable strength.
Traditionally independent bottlers were the most enthusiastic proponents of single casks but recently more and more distilleries have begun releasing their own single cask releases (some might even be with a participating retailer such as ourselves).