Is there a mach3 plug-in for Mach4 to control Mach3 controllers? I've looked in the plug-in forum sections. I've got a cnc machine with a Mach 3 controller and only wanted to get one version of software in case I wanted to upgrade later. Thanks.

No.  But what do you mean by controller?  If a motion controller there may be a Mach4 plugin for it. For example I use the UC100 controllers with Mach3, but if I upgrade to Mach4 I'll need to use the appropriate Mach4 plugin.  It depends if your controller supplier has developed the Mach4 plugin.

Yes I was looking for a Mach4 plug-in for a Mach3 motion controller. I did not realize I needed to check with the manufacturer.

What controller do you have?  As I understand it, the controller mfr signs an NDA with Artsoft to get access to the Mach4 (or Mach3) API and develops the driver (i.e. plugin) for their controller.  I think Artsoft and the mfr can distribute the drivers.  I know that for the UC100 that CNCDrive have plugins for M3 and M4 and when I bought them I downloaded them from CNCDrive.  Artsoft also supply them.

So the question is, if you are using Mach3 now with a motion controller, is there a Mach4 plugin for it?