Blender
Blender is a free, open-source tool for creating and animating 3D content. It is available for all major operating systems. It allows the creation and modification of graphics primitives, surfaces, etc. along with lighting and dynamic camera features. Animating is done via keyframes, and most properties can be animated over time. Advanced features include interactivity (e.g., game-like features), particle systems, skeleton-based models. Blender includes and is partially based upon a Python scripting system.