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.
Conic Planet is a CGI application which renders a photo-realistic real-time image of the Earth and other planets. It has support for Azimuthal, Mercator, Mollweide, Orthographic, and Rectangular projections. It also shows the current cloud covering.