Crystal City is remake of Targ (Exidy 1980). I made this game in course 'Game Development Challenge' in University of Jyväskylä. See more (in finnish): https://webapps.jyu.fi/wiki/display/pelihaaste/Peli+1%3A+Targ-klooni
You can play Crystal City here: http://users.jyu.fi/~elmakera/CrystalCity/ Original Targ: https://archive.org/details/arcade_targ