OSPRay is described as 'Intel OSPRay is an open source, scalable, and portable ray tracing engine for high-performance, high-fidelity visualization on Intel Architecture CPUs' and is an app in the Development category. There are four alternatives to OSPRay for Linux, Mac, Windows, Blender and Self-Hosted solutions. The best alternative is Mitsuba, which is free. Other great apps like OSPRay are Radeon ProRender (Free, Open Source), YafaRay (Free, Open Source) and OptiX (Free).
Physically based renderer. Mitsuba is an extensible rendering framework written in portable C++. It implements unbiased as well as biased techniques and contains heavy optimizations targeted towards current CPU architectures.
YafaRay is a free open-source montecarlo raytracing engine released under the LGPL 2.1 license. Raytracing is a rendering technique for generating realistic images by tracing the path of light through a 3D scene.
OptiX provides a simple, recursive, and flexible pipeline for accelerating ray tracing algorithms. Bring the power of NVIDIA GPUs to your ray tracing applications with programmable intersection, ray generation, and shading.