MacDraft allows you to create concentric circles simply by clicking any existing circle. Click and hold the mouse on the Circle tool and you will see a choice of circle tools, choose either diameter, radius or 3 point and create a circle in the document. Once the circle is placed, return to the circle tool, hold down the mouse, and choose the Concentric Circle tool. You can now click the circle you drew to create a new circle, offset from the original. The circle drawn will appear as a new object above the original so if it is bigger and has a fill you may need to move it back or bring the original to front.