All of the control programs I am familar with have what is known as MDI mode or Manual input mode. This is like a simple command line type of operation where you might enter G0 X2 Y3
and the machine would move to that position. This is a simple explination.
My favorite is TurboCnc (www.dakeng.com) which is a low priced, DOS based program that will run on just about any dos based machine.