D20 Omega World/GammaWorld: Master's of the Earth Campaign Setting

User summary: D20 Omega World/GammaWorld is an adaptation of the d20 Version of Gamma World and an extensive article appearing in Polyhedron #153 (Omega World by Jonathan Tweet). It includes numerous revisions and changes. From the introduction: Game Premise: The Omega World/GammaWorld begins approximately 200 years after The Black Days, which is what the present inhabitants of the devastated lands of Omega World/GammaWorld call the short period of plagues and wars that ended the age of man.