S-ray is a free photorealistic renderer based on monte carlo ray tracing.

It is capable of simulating all interactions of light with the environment, or L(D|S)*E paths in path notation. What this means is that it can simulate global illumination effects such as indirect diffuse illumination, caustics, and accurate reflection and refraction.

Here is a more or less complete feature list:

• Indirect diffuse illumination and caustics.
• Reflection and refraction from perfect and imperfect (glossy) surfaces.
• Area lights casting shadows with penumbra regions (soft shadows).
• Motion blur.
• Adaptive supersampling.
• Hierarchical keyframe animation.
• Simple XML scene description format, with converters from popular 3D file formats.

A lot more features are planned for the near future, check out the ToDo list.

To start playing around with s-ray see: GettingStarted