ImageJ is an image processing program inspired by NIH Image for the Macintosh. It can display, edit, analyze, process, save, and print 8-bit, 16-bit, and 32-bit images. There are modules for biology, astronomy, nuclear medicine, physics, and more. If you can take a picture of something, whether with a microscope, a telescope, an oscilloscope, an xray machine, or a scanner, then this program will let you enhance, manipulate, and measure the results.
wmJupiter is a Window Maker applet which features the planet Jupiter. It allows you to keep track of the Great Red Spot and the current distance in astronomical units (AE). The four Gallileo moons (Io, Europa, Ganymede, and Calisto) are also displayed when they are near the planet.