It is based on the science fiction horror film Aliens. Notable features of Aliens Online included asymmetric teams, teams consisting of more players than found in most first-person shooters of its era, job/class specialization, and its RPG elements. Players could fight on either the side of the United States Colonial Marines or on the side of the Aliens. Scenarios were played in one of six different types of terrain sets, with upwards of twenty to thirty players per side during each instance. Source: Wikipedia, "Aliens Online", available under the CC-BY-SA License.