David A. Hargrave's the Arduin Grimoire, that is. It was the first "cross-genre" RPG setting ever published. Sound familiar? Here are some of the classes Arduin introduced to DnD: Courtesan, Martial Artist, Merchant, Star Powered, and Techno. And don't forget his monsters: Air Shark, Kill Kitten and Screaming Scarlet Itchies. Arduin adventures encompassed interstellar wars, historical drama, and spine tingling horror. It is, in short one hell of a setting.
The Arduin Trilogy is composed of the Arduin Grimoire, Welcome to Skull Tower, and the Runes of Doom. These works gave us the world of Khaas, the legendary lands of Arduin. Hargrave eventually was served with a Cease and Desist order from TSR for using direct references to DnD. Know what he did? He used white-out and typing correction tape to remove the references and reprint the Grimoire.
Mr. Hargrave sadly passed away in 1988, but his work is still being published today through Emperor's Choice. A new system to go with the setting has also been designed. Long live Arduin and Khaas and everything they stand for.