x is a science fiction space trading and combat simulator series created by german developer egosoft. the series is set in the x-universe where several races populate a number of worlds connected by jumpgates. the games feature free roaming gameplay with trading, combat, empire building, and missions; leading to the series' phrase: ""trade, fight, build, think"". the series, which was launched in 1999 on the windows platform, consists of five base games: "", "", "", "x rebirth", and "". "x rebirth" introduced a new rendering engine as well as a new plot, one which "x4: foundations" now extends the storyline beyond ten years after the events in "x rebirth".