Blender is the open source, cross platform suite of tools for 3D creation.
- For 3D Designing - For 3D Modeling - For 3D Rendering - For 3D Game Designs - For Quality Time Pass (Fun) - For 3D Animation and Video Making (eg. Open Peace Movie Project - Big Buck Bunny)
Blender is available under GNU/GPL, for most OSes. The OpenGL and OpenAL integration makes it's interface tough to understand at first but you'll find it quite easy once you get familiar to all those Hot Keys for different functionality in Blender.
Blender supports Python Scripting. Scripts can be used to produce special effects in modeling.
- Get familiar with the Blender Keyboard Short Cuts. - Try out with some example designs.