Mac users interested in 123d free by autodesk generally download:
Create and edit 3D models on your Mac. Generate them from scratch or access a huge library of pre-built models, choose textures, and export your projects as STL files. Build 3D models from multiple images taken at various angles, sculpt objects, work with mesh models, and 3D print.
Build 3D models and implement the created constructions in real life. Import a file in STL or OBJ format and select to generate a layered, interlocked, or folded assembly design. Work with such materials as cardboard, plywood, paper, and plastic and print your shapes on regular paper to use as a guide.