iSextant is a sun sign reduction program, that can be used to confirm your location in the event of GPS signal problems. It is reported that in 2010-2011 due to high solar activity there will be increased chance of GPS outage.

iSextant can also be used as an aid to learning astro-navigation.

It requires that you take a sun sight using a Sextant and note various other conditions, such as pressure and temperature. Using this information along with an assumed position the program with give you GHA, Declination of the Sun followed by an Azimuth and Intercept from your assumed position.

For more information about astro-navigation please refer to http://en.wikipedia.org/wiki/Astro_navigation.