LiquidMaya is a Maya to Renderman plug-in that handles full Renderman output support with a focus on speed, efficiency, and extensibility. Its features include procedural rib generation, full network rendering support, segmented rib files, a shader assignment interface, and much more. Along with the ability to write full C++ plug-ins, it is incredibly easy to script Liquid with Mel. Liquid was used for the visual effects of the "Lord of the Rings" movie.
