LuxRender is a free and open source software rendering system for physically correct image synthesis. The program runs on Linux, Mac OS X, and Microsoft Windows.

LuxRender features a 3D renderer; it relies on other programs (3D modeling programs) to create the scenes to render, including the models, materials, lights and cameras. This content can then be exported from the application it was created in for rendering using LuxRender.

Fully functional exporters are available for Blender, DAZ Studio; partially functional ones for Cinema 4D, Maya, SketchUp and XSI. Luxrender is also fully supported as production renderer in 3DS Max. After opening the exported file, LuxRender renders the scene. Various tweaks to post processing settings can be set via graphical user interface and the scene control file. A significant feature of LuxRender is, that the user is able to change the balance of different lights while the image is still being processed.

For more information:

https://en.wikipedia.org/wiki/LuxRender