LuxRender (64-bit) is a physically based and unbiased rendering engine. Based on state of the art algorithms, LuxRender simulates the flow of light according to physical equations, thus producing realistic images of photographic quality.
LuxRender is free software - both for personal and commercial use - and is licensed under the GPL. The program runs on Windows, Mac OS X and Linux. Fully functional exporters are available for many popular 3D packages.