The guy that coded z3ta went on to be part of Cakewalk and coded Rapture and Dimension, and in some ways/features they both go beyond what z3ta did, and in others don't go quite as far. Neither sound as good as z3ta imo.
z3ta wasn't the be all and end all of synths, but it was a nice instrument that had a powerfully simple gui and most of all it sounded very good indeed - certainly is up there as one of the best sounding software synths made to date, imo.
Yes, I can run it in Windows, but it's not really the best workflow solution. Occasionally I dig out the M$ and play z3ta and remember just how nice it is... I'll probably end up multisampling out some of my favourite patches as a workaround...