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.
Floorplanner - Floor plan interior design software. Design your house, home, room, apartment, kitchen, bathroom, bedroom, office or classroom online for free or sell real estate better with interactive 2D and 3D floorplans.
Mach3 - Mach3 is very popular among the Hobby CNC community.
Sweet Home 3D - Sweet Home 3D is a free interior design application that helps to draw the plan of house, arrange furniture on it and visit the results in 3D.
PyCAM - PyCAM is a toolpath generator for 3-axis CNC machining.
SketchUp - 3D for Everyone