Frink is a calculating tool and programming language designed to help you in the real world. It tracks units of measurement throughout all calculations and ensures that answers are correct. It converts between systems of measurement, and has a huge library of physical data. It is both a simple calculator for quick calculations and a full-fledged programming language for large tasks. It draws high-quality graphics, handles conversions between time zones, currencies, and historical values of the U.S. dollar and the British pound, translates between several languages, does date/time math, and more.
Lynkeos processes astronomical webcam images. By stacking the best images, the signal to noise ratio is increased, and details lost in the noise of individual images become visible in the resulting image. This software accepts, as input, QuickTime, AVI, and MPEG sequences, or still images, in any image format supported by its active plugins (TIFF, FITS) and Cocoa. It generates a 16-bit RGB TIFF or a monochrome FITS image as output, to be further processed with some all-purpose image processing application.
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.
CFITSIO is a library of C and Fortran subroutines for reading and writing data files in the FITS (Flexible Image Transport System) data format. It simplifies the task of writing software that deals with FITS files by providing an easy to use set of high-level routines that insulate the programmer from the internal complexities of the FITS file format.
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.
Qastrocam is a capture program that can work with any video4linux device. Its main purpose is to do astrophotography. It can control a telescope to do guiding with the images received from the video device. It can also control the extended features of a webcam modified to do long exposure (several seconds) captures.