Sculpting (free)
Sculptris
Sculptris is an elegant, powerful and yet easy to use 3D sculpting software, allowing the artist in you to simply focus on creating amazing 3D artwork. Gone are the technical and often tedious constraints typically associated with digital art. If you're new to the world of digital sculpting, Sculptris is the ideal ground on which to get started. If on the other hand you're experienced in CG, what you will find in Sculptris is a blazingly fast way to realize your concepts. It's intuitive, fun and user friendly, so you can focus as an artist on pure creativity.
123d
Autodesk 123D is a hobbyist CAD and modelling tool created by Autodesk. It is similar in scope to Google Sketchup and based upon Autodesk's Inventor product range. As well as the more basic drawing and modelling capabilities it also has assembly and constraint support and STL export. Available for the software is also a library of ready-made blocks and objects.
