Desktop Applications

Sky & Telescope's Jupiter's Moons JavaScript utility.
For any date and time from January 1900 through December 2100, this interactive tool shows the positions of Io, Europa, Ganymede, and Callisto. Moreover, the utility matches the view in your telescope's optical system, whether it shows the sky with north up, south up, or mirror reversed. And it tells you when the moons (and/or their shadows) are crossing the planet's disk, hidden behind it, or eclipsed by the planet's shadow.

Stellarium - Free
Possibly the only software you will ever need -and the price is right! Combination of comprehensive star atlas/chart/planetarium/telescope control program. Simple to use, but like anything else you need to study the instructions to get full use out of it.

TheSkyX - $329
The SkySix Professional Edition is used by more observatories and controls more automated telescopes than any other astronomy software. For twenty five years, astronomers worldwide have relied on TheSky for everything from a visual observation guide to turn-key telescope control center. The Sky6 Professional Edition has extensive databases of celestial information.

TSatellite Tracking Software - Free
For tracking and following artificial satellites.

STARALT - Free
The program, Object Visibility- STARALT, is provided by the Isaac Newton Group of Telescopes. Staralt is a program that shows the observability of objects in various ways: either you can plot altitude against time for a particular night (Staralt), or plot the path of your objects across the sky for a particular night (Startrack), or plot how altitude changes over a year (Starobs), or get a table with the best observing date for each object (Starmult). You can select an observing site from a list of international observatories or use the coordinates of your own site (Your backyard, for example). You can also enter multiple objects.