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.
The Doomsday Engine is a modular game engine and source port for classic FPS games (Doom, Heretic, Hexen, Doom64) with client-server architecture. It provides enhanced rendering (OpenGL), audio systems, GUI frameworks, networking, and scripting capabilities. The engine supports extensibility via plugins and includes tools like Amethyst for documentation processing. The codebase shows strong separation of concerns with distinct libraries for core functionality, game logic, rendering, and UI. While actively maintained, it exhibits technical drift due to platform-specific conditionals, legacy code sections, and complex dependency management.