123D is a free solid modeling software program based
on the same Autodesk technology used by millions of designers and
engineers worldwide. Not an engineer? No problem, with Autodesk 123D
you can design precise and makeable objects using smart tools that let
you start with simple shapes and then edit and then tweak them into
more complex shapes.
This new application has its focus on 3D printing, paper models and engineering prototyping.