Some free computer-aided design software options are MINOS, DoubleCAD XT, Draft It, FreeCAD and Autodesk 123D. MINOS is a solid modeling software for Windows. It uses a technology that links simple geometric elements to form contours. Users can turn these contours into three-dimensional shapes by extruding, revolving and sweeping them. They can combine these 3D shapes to create complex geometric shapes.
DoubleCAD XT is two-dimensional CAD software that is compatible with DWG and SKP formats. It offers features such as self-healing walls, transparent fills, object snap prioritization, advanced polyline editing and hatch pattern editor. It is available for Windows-based PCs.
FreeCAD is an open source parametric 3D modeler with which users can design real-life objects. This software works on Windows, Mac OSX, BSD and Linux platforms, and it is compatible with a wide range of file formats, including STEP, IGES, SVG, STL and OBJ. It has an Open CASCADE Technology-based geometry kernel that supports 3D operations on complex geometric shapes. The objects in FreeCAD are parametric, and users can undo and redo changes easily.
Autodesk 123D Design is a 3D modeler for PC, Mac and iPad that supports 3D printing. It is part of a suite of free CAD and modeling software known as the Autodesk 123D.