From the website:

Art of Illusion is a free, open source 3D modelling and rendering studio. It is written entirely in Java, and should be usable on any Java Virtual Machine which is compatible with J2SE 1.4 or later.

The current version is 2.5, released Aug. 18, 2007. This version is both stable and powerful enough to be used for serious, high end animation work. Many of its capabilities rival those found in commercial programs. Some of the highlights include subdivision surface based modelling tools, skeleton based animation, and a graphical language for designing procedural textures and materials.