From the Publisher's Website:
Darwin's World is a role-playing game set in the wild, inhospitable world of mankind's ruin, after a series of devastating wars that brought the human race to the brink of extinction. In a world where radiation has altered the very course of nature, mankind has ceased to exist in its current form. Mutations and genetic variations are the edge separating a species from life and death.
New and Improved Survivor's Handbook!
The premier d20/OGL post-apocalyptic roleplaying game, Darwin's World 2nd Edition, is back in print. The same great rules, but now in a more useful format! The Survivor's Handbook contains all the player rules plus the relevant rules from the Modern System Reference Document, as well as expanded material previously available only in PDF.
Darwin's World 2nd Edition is focused on separating the mechanics from the setting, making Darwin's World the definitive guide to building post-apocalyptic campaigns, whether you are playing in the Twisted Earth or your own preferred post-Fall setting.