Pixie is an open source RenderMan renderer for generating photorealistic images.
Edit By BS Editor: Pixie is an open source RenderMan renderer for generating photorealistic images. You can compile Pixie on Windows (using Visual Studio 2005), Linux and on OSX (using XCode or unix style configure script).

Features:
Object instancing / delayed primitives
Displacements
Programmable shading (using RenderMan Shading Language)
High quality texture/shadow/environment mapping
High dynamic range input/output
Scalable, multi-resolution raytracing using ray differentials
Pixie now has a new raytracing engine that automatically tesselates surfaces on the fly to a desired accuracy determined using the ray differentials. This means rays tracing blurry reflections or computing global Illumination are FASTER to trace and sharp reflections and shadows are more accurate. Pixie also contains a memory manager that keeps the memory that is used to keep these tesselations around under control. Similar to texture caching, Pixie will maintain a set of active surfaces and only those surfaces will consume raytracing memory.
Motion Blur
Depth of field
Level of detail (LOD)
Reyes style rendering (very fast)
Occlusion culling
Network parallel rendering
DSO shaders
Global illumination you can free download Pixie 2.2.6 now.