The One Roll Engine (ORE) was designed by Greg Stolze and popularized by the GODLIKE, WILD TALENTS, REIGN, and NEMESIS rule sets. In the system, all actions are decided by a single roll of the dice, rather than separate rolls for initiative, success, and damage. This system allows for great flexibility and speed of play.
Provided are some links to ORE rules sites, modifications to rules, and guides on using ORE to simulate Colonial Marines fighting Aliens.
Company Sites
  Fan Sites
  House Rules
  Aliens vs Colonial Marines--ORE Conversion (Wild Talents 2nd Edition)
  Unhallowed Metropolis--ORE Conversion