FreeCAD is a free open source 3D Modeling and Design Software for Windows, Mac and Linux. It is Parametric Modeling software so you can easily modify the design by going back into your model history and changing its parameters. It is released under LGPL License. It uses OpenCascade, CAD kernel, Coin3D, Qt and Python. It supports plugins to add extra functionality to the software. you can import and export to STEP, IGES, OBJ, STL, DXF, SVG, STL, DAE, IFC or OFF, NASTRAN, VRML and Fcstd file format. Some other features are Sketcher, Robot simulation, macro recording & editing, Drawing sheets and runs as a command line application.