Blender

Blender screenshots

Blender is a free and open source 3D animation suite
Main window
Blender 2.7 : Main window

Alternative downloads

ADA3D STL Viewer
Free program that helps you visualize STL or OBJ meshes.
1.4.0
FREE
Animate Me!
Animate Me! creates gif animations on the base of effects quickly and easy.
2.2
Maxwell Render
A rendering engine based on the mathematical equations governing light transport.
2.6.0.0