Appleseed – open-source physically-based rendering engine
2015 Interview with the lead developer: http://blenderdiplom.com/en/interviews/607-interview-francoi...Seems like it's in around the same place, although the plugins are getting better and the renderer is starting to support complex scene features (not quite there yet).Overall though there are 100's of ray-tracers and scene renderers (seemingly all in C++), so it's not clear if it has any compelling advantages.