One of the noted extrapolations of the Zone System is BZTS (Beyond the Zone System) It was concepted by Phil Davis, who wrote a book on it about twenty five years ago. Although Mr. Davis has passed away, it is still a current system used by many. More info is available here:
Originally Posted by starrykitten
The Zone System is touched on in may texts, old and new, but as a sensitometry method for B&W practice, it has never been immutable, however, almost all B&W photographers generally practice a personalized "Zone System" no matter if they call it that, or even recognize that they do.
Attempts have been made to "translate" the Zone System for d*g*t*l imagers, but since the two media behave in very different ways, it usually amounts to just hanging Zone System terms on basic sensitometry, or other types of mimicry, and has little to do with the St Ansel's system.