RenderMan is described as 'PhotoRealistic RenderMan, or PRMan for short, is a proprietary photorealistic RenderMan-compliant renderer' and is an app. There are more than 25 alternatives to RenderMan for a variety of platforms, including Windows, Mac, Linux, Sketchup and Blender. The best alternative is Cycles Renderer, which is both free and Open Source. Other great apps like RenderMan are LuxCoreRender, POV-Ray, Keyshot and V-Ray.
RenderMan is mainly a 3D Modeler but alternatives to it may also be 3D Animators. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of RenderMan.
Cycles is Blender’s ray-trace based production render engine and in development since 2011. It was originally developed by Brecht van Lommel, and is maintained by an active team of developers today. Since its release as Apache 2.
LuxCoreRender is a physically based and unbiased rendering engine. Based on state of the art algorithms, LuxCoreRender simulates the flow of light according to physical equations, thus producing realistic images of photographic quality.
The Persistence of Vision Raytracer is a high-quality, totally free tool for creating stunning three-dimensional graphics. It is available in official versions for Windows, Mac OS/Mac OS X and i86 Linux. The source code is available for those wanting to do their own ports.
V-Ray 2.0 for 3ds Max is a complete rendering solution, which combines the power of the well-known V-Ray award-winning production rendering engine with the flexibility and exceptional speed of the interactive rendering system V-Ray RT and the even more impressive new V-Ray RT...
appleseed is a modern, open source, physically-based rendering engine designed to produce photorealistic images, animations and visual effects. It provides individuals and small studios with an efficient, reliable suite of tools built on robust foundations and open technologies.