SaVi is satellite visualization software that lets you create, run, examine, and modify satellite orbits in two and three dimensions. Simulations of Iridium, Globalstar, Galileo, GPS, and other satellite constellations are included. SaVi requires Tcl and Tk on a system with Unix libraries. SaVi works well with the 3D renderer Geomview. Geomview is optional, though recommended for its 3D rendering capabilities.
Xplanet was inspired by Xearth, which renders an image of the earth into the X root window. All of the major planets and most satellites can be drawn, similar to JPL's Solar System Simulator. A number of different map projections are also supported, including azimuthal, Mercator, Mollweide, orthographic, and rectangular.
Gpredict is a real time satellite tracking and orbit prediction program. Besides the general orbital data for satellites, gpredict can also calculate the footprint, visibility, doppler shift, signal loss, and signal delay for each satellite relative to one or more ground stations. The calculated data can be viewed in tables, on maps, or on polar graphs.
Cactus is a general, modular, parallel environment for solving systems of partial differential equations. The code has been developed over many years by a large international collaboration of numerical relativity and computational science research groups and can be used to provide a portable platform for solving any system of partial differential equations.
Astronomy for fun (education, science, whatever). Nightfall is an interactive application to simulate eclipsing binary stars, and to produce animated views, synthetic lightcurves and more. Takes into account the non-spherical shape of close binary stars, mutual reflection, and some other effects. Comes with documentation, on-line help, and lots of observational data of real binary stars. Supports the Gnome desktop, but doesn't require it.
INDI is an instrument-neutral distributed interface control protocol that aims to provide backend driver support and automation for a wide range of astronomical devices (telescopes, focusers, CCDs, etc.). Current supported devices include many telescopes, CCDs, filter wheels, focusers, and video cams. INDI is used in popular astronomy suites like Xephem, KStars, DCD, and Cartes Du Ciel.
TRIP is a general computer algebra system dedicated to celestial mechanics. It includes a numerical kernel and has interfaces to gnuplot and xmgrace. Computations can be performed with double, quadruple, or multi-precision. Users can dynamically load external libraries written in C, C++, or Fortran. Parallel computations on multivariate polynomials can be performed.