FPrime is a popular previewing tool and rendering engine for LightWave 3D. Its rendering method is unique in the fact that it continuously refines images until the user manually specifies that the image is of adequate quality. This is opposed to traditional rendering methods in which the image being rendered cannot be refined by the renderer once completed.
FPrime is widely considered to be much faster than the native LightWave rendering engine, allowing for real-time previews of computationally intensive effects such as global illumination and node-based surfacing. Although currently the native Lightwave Engine (9.5+) is at a par in regard to speed, the workflow for texturing and lighting using FPrime is still unrivaled.
FPrime is developed by Worley Labs and is currently at version 3.5.