Donald E. Westlake: Anarchaos (2004)
From the Publisher:
Anarchaos was a planet, inhabited by humans, where anarchy was the only law; where each man protected himself as best he could; and where the weak were soon dead. Malone's brother had died that way, and Malone had come to Anarchaos, carrying a small arsenal of weapons, to find the man who had killed him. He knew that he was facing an entire planet of enemies.
Donald E. Westlake: Anarchaos. Severn House, ISBN: 0727860968 (May, 2004), 144 p., $27.25, £17.99