Brotherhood is a retro-shooter inspired by Wolfenstein 3D, developed by FatCatGames. The game is set in a secret scientific complex within an ancient prison, where players must steal weapons and obliterate a religious brotherhood that experiments on humans. Players take on the role of a test subject immune to mutagens, harnessing this power for near-indestructibility. The gameplay involves exploring one-story levels, collecting items like first aid kits and key cards, and engaging in firefights against numerous enemies.

The game features over 20 enemy types and 9 weapon types, including a shotgun, laser rifle, flamethrower, rocket launcher, and a secret weapon called "Butterfly". Players navigate 24 levels across 6 acts, encountering traps and environmental hazards. The Brotherhood aims to replicate the classic old-school shooter experience with its level design, weapon variety, and hidden secrets.