Radeon ProRender is an easy to use, physically accurate renderer running on OpenCL. the renderer is free, open source, and cross-platform. It has the ability to scale, using AMD XConnect.
ProRender currently has plugins for 3ds Max, Maya, Rhino and Solid Works.
Here, Antonio offers a look at how you create physically accurate materials ProRender. The video and mentions “AMD FireRender”, that is what ProRender was formerly known as.
This is a good look at observing real-world materials and trying to replicate them in render.