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.
Earth orbits and satellite coverage display in 3D on your laptop.
SaVi - simulate Starlink, Iridium, Globalstar, O3b, GPS, Galileo and other satellite constellations, modify them, or design your own. Requires Tcl/Tk and Unix libraries; 3D viewing option requires Geomview running on X Window.
tkBacktracer is a cross-platform interactive visualization tool to explore the tool motions in RS-274D "G-code" CNC files used in computer controlled milling and manufacturing.