LinuxCNC (the Enhanced Machine Control) - LinuxCNC: an open source CNC machine controller. It can drive milling machines, lathes, 3d printers, laser cutters, plasma cutters, robot arms, hexapods, and more.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Mach3 - Mach3 is very popular among the Hobby CNC community.
FreeCAD - An open-source parametric 3D modeler
PyCAM - PyCAM is a toolpath generator for 3-axis CNC machining.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming