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.
Z88 a free finite elements program featuring 20 different element types for LINUX and Windows. Includes two solvers, a mesher, plot programs and a GUI with online help.