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.
MultiSeti is a utility for the Seti@Home client which helps you manage multiple SETI packets. If you have dial-up access to the Net, want to download more than one packet, and don't want to run clients simultaneously, MultiSeti will run one after another (when one is finished analyzing, it starts seti to analyze the next packet).
libAstronomy provides a set of astronomical routines to ease the calculation of ephemerides. It includes mathematical functions to compensate various astronomical phenomena like precession, nutation, etc. The getconstellation routine finds the constellation for a given coordinate. It also calculates the positions of the sun and moon in two different precise ways.