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.
Xgravity is a program for the simulation of 3D gravitational motion of n-bodies. It reads a file with the current state of the bodies, and displays the motion. It features a nice isometric perspective, Red-Green stereographics, and a stereographic perspective which allows you to see the trace in "real" 3D. There is a GTK GUI interface in development, which gives you the ability to perform basic operations with the system, like modifing objects, rotating, eliminating drift, and launching a simulation.
COSMIX is a general purpose N body integrator. It allows simulation of the behavior of gravitational systems according to different physical theories. The current release is only a test release - it only supports the newtonian approximation. The project aims at tackling relativity in coming releases.
Astro Info is an astronomical ephemeris/almanac for PalmOS. It displays some basic information useful to stargazers, such as rise, trans, and set times, coordinates, magnitude and phase information for Sun, Moon, and the other 8 planets and stars. It can display a view of the sky (with stars, the Sun, Moon, and planets positioned) at arbitrary times and locations. You can also search for objects based on their names and see where they are.
UFOClock draws an astronomical clock. From it you can read the time of day, phase of the lunar month, ratio of day to night, time until a solstice or equinox, and time until the end or beginning of twilight. The time of day depends on your location on the surface of the Earth, which you can enter on the command line or in a dotfile in your home directory. Location can be given as latitude/longitude or ZIP code. It is called UFO clock because it sort of looks like crop circles. It is based on Sundial by George Williams. It requires GLUT installed to run and the NOVAS library to build.