You might look at Kerkythea. It hasn't been updated in a while, though a new version is supposedly on the way. It is fairly unique AFAIK, in supporting multiple rendering algorithms including raytracing, photon mapping and path tracing; so you can play a bit with the different methods. PoseRay will convert Poser scenes (mesh and basic materials only) to Kerkythea format for rendering.

http://en.wikipedia.org/wiki/Kerkythea

http://www.kerkythea.net/joomla/index.php 

https://sites.google.com/site/poseray/ 

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