FreeCAD is a parametric 3D modeler made primarily to design
real-life objects of any size. Parametric
modeling allows you to easily modify your design by going
back into your model history and changing its parameters. FreeCAD is
open-source and highly customizable, scriptable and extensible.
FreeCAD is multiplatfom (Windows, Mac and Linux), and reads
and writes many open file formats such as STEP, IGES, STL, SVG, DXF,
OBJ, IFC, DAE and many others.