Mach3 is PC-based CNC software

http://www.machsupport.com/

How to connect KMtronic 2 relay board for your Mach3 CNC project

https://info.kmtronic.com/how-to-connect-kmtronic-2-relay-board-to-your-mach3-cnc-project.html

How to control KMtronic USB relays from Mach3

https://info.kmtronic.com/mach3-and-kmtronic-usb-relays.html

KMtronic USB relays & Mach3 - step by step

https://info.kmtronic.com/kmtronic-usb-relays-from-mach3-step-by-step.html