Persistence Of Vision is an SDL (Scene Description Language) for 3D rendering engines, not that different from what USD is to the Renderman community.
With a long history that makes it very stable and feature rich, its main engine is rewritten since v3.7 (currently 3.8) with 64 bits multi-threading, subsurface scattering, stochastic quasi Monte-Carlo sampling, depth of field, real time mode…