User summary: The Masters of the Earth game is a heavily customized implementation of d20 Modern System intended to support campaign play in the "Masters of the Earth" setting, itself a customized implementation of Gamma Terra. The Masters of the Earth game has a long development history. The campaign setting ante-dates the game system, and originally was used with Gamma World. The current version of the game is available for free download. The game is published as a series of 38 PDF documents organized by topic. Each document has a separate revision history and publication date. The game's primary development occurred 2003 - 2005.