CorsixTH is a comprehensive open-source reimplementation of the 1997 Bullfrog game Theme Hospital. It reconstructs the original game's mechanics faithfully using a C++ engine for performance-critical subsystems (rendering, audio, pathfinding, file I/O) and Lua scripting for game logic, UI, and data definitions. The architecture is a monolithic desktop application with separate utility tools (a Java level editor, a wxWidgets animation viewer, and a sprite encoder). The Lua codebase is extensive, featuring a custom class system, humanoid action queue pattern, room/object definitions, localization support, and a persistent save/load system. The game runs cross-platform on Windows, macOS, Linux, and BSD via SDL3. Notable reusable patterns include a lightweight OOP framework (class.lua), a generic pathfinder with multiple search strategies, a virtual filesystem abstraction, and an RNC decompression library. The project is actively maintained with CI, issue templates, and a large community, though some subsystems (e.g., movie player, MIDI) rely on optional dependencies.