Aqsis is a high quality, photorealistic, 3D rendering solution. It complies with the RenderMan interface standard defined by Pixar.

The RenderMan standard has been used in film and television visual effects since it's introduction in 1989. Pixar has used their own implementation for all of their award winning CG features, and provided their implementation for use in the visual effects of most major blockbuster films over the last 2 decades. The Aqsis project offers a way for individuals and organistaions alike to gain experience with the RenderMan® interface without the cost of commercial software licenses.

Aqsis comprises a command line rendering tool, a tool for compiling shaders in the RSL language, a tool for preparing textures for optimal use, and various developer libraries to enable integration with third party tools.

Why use Aqsis
Aqsis is Open Source
Therefore, not only is it free to use, but you can make modifications yourself if it doesn’t quite fit your specific requirements.
Aqsis is based on RenderMan
The basis on which Aqsis is built has a long history of use in all area’s of the CG industry. Through its RenderMan® heritage, it provides some key features that are important particularly in high end CG production, such as depth of field, motion blur and programmable shading.