And you can download it right here, for Mac, Windows, Linux, OS/2, and other open operating systems. About:

Mars24 is a Java application which displays a Mars sunclock, a graphical representation of the planet Mars showing its current sun- and nightsides, along with a numerical readout of the time in 24-hour format. Other displays include a plot showing the relative orbital positions of Mars and Earth and a diagram showing the solar angle and path for a given location on Mars.

Created at NASA's Goddard Institute for Space Studies.

And for iOS, this looks promising. Haven't tried it, and it's not a NASA product, so YMMV.