Hey Greg,
the breakout board adapter is nothing than a 25-pin D-Sub to screw terminal adapter. It can be used on any device that has a 25-pin D-Sub port. Such adapters are a standard electronics part and are available everywhere.
On the 
Onefinity Original Series Controller, it allows you to attach devices like optocouplers, relays or sensors in order to be able to e.g.
- automatically control router on/off with M3/M5
- automatically control dust collector on/off with M3/M5
- automatically control workpiece coolant pump on/off with M7/M8
- to have a serial communication with a VFD/spinde that is ModBus-compatible
- to have analog speed control of a PWM spindle
- to retrofit inductive proximity sensors as limit switches to the machine to no longer have to use stall homing
Here you find the pin assignment of the 25-pin I/O port on the Onefinity/Buildbotics controller.