This is a review of some astronomy software, as used on the Earth in the early 21st Century, by a somewhat geeky chap. In this episode, I talk a little about two astronomy apps available for Android and another two available for GNU/Linux (and other) desktops.
Erratum: I referred to Star Map but I meant Star Chart. Doh!
In reverse order of how much I use and like them (most used/liked last):
http://www.stellarium.org - Available for all major operating systems. This link shows you how to add your own comets: http://www.wikihow.com/Add-Comet-ISON-to-Stellarium
http://edu.kde.org/kstars/ - KStars is part of the KDE SC Software Compilation) and so will be easy to install if you're a KDE user, or if you're not, "easy" after a few dependencies are installed.
Google Sky Map can be installed on your mobile device using either f-droid or Google Play: https://f-droid.org/repository/browse/?fdfilter=sky&fdid=com.google.android.stardroid https://play.google.com/store/apps/details?id=com.google.android.stardroid
If you like eye-candy, then Star Chart may be for you, get it on Google Play here: https://play.google.com/store/apps/details?id=com.escapistgames.starchart