Trade with other civilizations in minerals, technology, food and drugs. More than 30,000 objects in the X universe. The original working title was just X for most of the time. First, it just sounded cool, then it got more and more different meanings. Like for example, all the things that X could stand for, just like in an equation.
X stands for action as well as strategy, building, trading etc.
Whatever the player wants. Our game supplies the universe, what the player makes of it is up to him or her. In the first place, X is a game that tries to give as much freedom of gameplay to the player as possible. So, the linear plot or story that the game evolves around is just one of many possible things to do. The story for the plot of the game grew ontop of that later.