PxrVCM extends this with bidirectional path tracing. In addition to the paths from the camera, it traces paths from the light sources and tries to connect them. It can resolve complicated indirect paths that may be slow to converge with PxrPathTracer. In particular, it is designed to handle specular caustics. Caustics are an effect of light being refocused after reflecting or refracting off a surface. The above image illustrates both of these effects. If your scene requires these effects or you have complex lighting where some lights may be covered or hidden in fixtures, then the PxrVCM integrator is your most likely efficient choice.
PxrUnified is available but currently experimental until it supports all the features of commercial RenderMan.
PRMan includes example RIB files and shaders demonstrating the integrators, at the heart of RenderMan. These examples can be found in the /lib/examples/RIS/scenes directory of your RenderMan Pro Server installation, in the /spt and /vcm subdirectories. Some of the examples are discussed in detail in the pages below. Whether or not you're inclined to open up a terminal window and render along, these pages serve as a broad overview of the features and capabilities of PRMan.