Some machines use a controller, others use a computer.
Controller can be a vague term when it comes to CNC, as people use it to describe a lot of different things.
Basically, every machine needs machine control software.
These come in many flavors.
Mach3 and Linux CNC are software controls, meaning they can run a machine directly from a PC with just the software, through a parallel port.
Both of these can also use additional hardware to generate step pulses, and provide additional I/O. The additional hardware will improve performance capabilities.
Then you have the software + hardware controls. Mach4, UCCNC, Centroid Acorn, EdingCNC, ...
These have a software program that runs on a PC, but also use additional hardware to control motion and handle I/O. Some of these do all the calculations in software, and some use external hardware to do the motion calculations.
Then you have the standalone all in one controls, which include a number of Chinese options (including Axiom), and the Masso. These don't require a PC at all. Some have their own displays, and some require a separate monitor.
All have their strengths and weaknesses, and the choice will often depend on what features one needs. The Software + Hardware options tend to have a lot more features, and have more customization options.
Mach4 is very capable, and a big step up from Mach3.
The people that don't like it are usually former Mach3 users. Mainly because it's very different from Mach3, and customization is more complex. But Mach4 is far more powerful, and provides much better motion than Mach3.
Since Mach4 is what AVID CNC sells, they also support it, and they provide excellent support. This is a big plus.
As for Macs. :surprise:
Mach4's system requirements do not mention macs. And I've not heard of people using it with macs. If they are, it's probably with Bootcamp.
My recommendation for running Mach4 would be to buy a new, mini PC running Windows 10, similar to this.
Many people run Aspire on macs using parallels or bootcamp. You can then send your g-code to the mini PC via wifi.
I'd recommend joining the Vectric forum and asking any mac questions there.