In the forum, I find various references to "Mach4" my own Mach3 even pops-up "Mach4" error messages. Is there a version 4 available somewhere?

Mach4 was going to be the next version of Mach a year or two back, then the name was changed to Quantum. Finally Art decided to add the functionality to Mach3 so there is no more Mach4 or Quantum. The next big step will be Mach3 Rev4 which has a lot of changes in it but when that will be out just depends on how much time Brian gets on it instead of trying to fix things in the present revisions.
Hood