BRL-CAD is a powerful cross-platform constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing for rendering & geometric analyses, network distributed framebuffer support, image & signal-processing tools.
LDraw utility for creating replacement minifig head .DAT part files with inline POV code for improved renderings in POV-Ray. ML-Cad or your LDraw editor of choise will ignore the inline code and show the parts just as before.