PowerMill - PowerMill is an advanced CAM software that comes with a flexible way to get done with your complex high-speed and five-axis machining processing.
FreeCAD - An open-source parametric 3D modeler
SOLIDWORKS CAM - SOLIDWORKS CAM is an add-in that provides you the leverage of computer-aided manufacturing, allowing you to generate g-code and m-code for CNC machining of different parts.
SketchUp - 3D for Everyone
MeshCAM - MeshCAM is the fastest way to generate gcode
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.