X-plorers is an adaptation of the original Dungeons & Dragons rules to a science fiction setting. From Grey Area Games:

In the year 2,222 AD Earth, Venus, and Mars are united under one government, the United Corporate Nations (UCN). The UCN is a political engine composed of representatives of thousands of powerful corporations. Far beyond our solar system lies the “Reaches”, a densely packed cluster of stars, many with habitable worlds very similar to Earth. The UCN is looking for both habitable planets and those ripe for resource exploitation. Such a vast and new galaxy breeds nothing but trouble. Who better to handle such trouble but the galactic troubleshooters…X-plorers X-plorers is a “what if?” role playing game. In this case, what if the fathers of the role playing hobby were more into science fiction than fantasy when they wrote that first set of official rules back in 1974? What if that game was about humans expanding and exploring their universe, instead of delving into deep dungeons to kill monsters to earn treasure? These are the questions X-plorers attempts to answer.