FreeCAD is free multi-platform CAD software to create 3D models. FreeCAD can be used in the technical design, construction products, as well as in other areas relating to the implementation of engineering work.
The program is good free alternative to create models for 3D printers as it supports STL format. Besides its own program FreeCAD formats are compatible with the following formats: DXF, SVG (Scalable Vector Graphics), STEP, IGES, STL (STereoLithography), OBJ (Wavefront), DAE (Collada), SCAD (OpenSCAD), IV (Inventor), and IFC. The application is a good free alternative to AutoCAD.