Blue Moon Rendering Tools by Larry Gritz is a free collection of high quality rendering programs which adhere to the RenderMan interface standard. Programmable shading, ray tracing, radiosity, motion blur, depth of field, volume shaders, and other advanced features are supported. RenderPark is a software package from the computer graphics research group at Katholieke Universiteit Leuven, in Belgium. Frame rates of 15 fps have been achieved for non-trivial scenes. It runs about 3 times faster than POV-Ray, though is nowhere near as full featured.
Source code is available.
The Standard Procedural Databases package is a set of C programs for testing the efficiency of ray tracers and other rendering algorithms. It includes programs for tessellating the teapot, creating fractal terrain, growing trees, etc., along with some basic 3D file format converters and displayers. Radiosity RenderPark is a software package from the computer graphics research group at Katholieke Universiteit Leuven, in Belgium. 11 test scenes from the 5th Eurographics Workshop are available for download. These diffuse, grey environments are designed for testing radiosity and Monte Carlo algorithms.