Yamagi Quake II is a conservative source port of id Software's Quake II, focusing on offline and cooperative gameplay while maintaining compatibility with the original game data. The codebase implements a full client-server architecture with multiple rendering backends (OpenGL 1.x, OpenGL 3.x, software), OpenAL/SDL sound, input handling (keyboard, mouse, gyro), and network protocols. The game logic includes complete monster AI, weapons, items, and multiplayer support. The project is written in C and organized into client, server, game, and common modules, with platform-specific backends for Unix and Windows. It is GPLv2 licensed and community-driven.