flow5 is a comprehensive desktop application for preliminary aerodynamic analysis and design of 2D airfoils, 3D aircraft configurations, and sailing vessels. It implements multiple potential-flow solvers: XFoil for viscous 2D analysis, and 3D panel methods (VLM, LLT, QuadPanel) coupled with wake models and boundary-layer corrections. The application provides a full-featured GUI built on Qt with OpenGL 3D views, interactive geometry editors (splines, NURBS, STL, OpenCASCADE), and extensive plotting capabilities. It supports batch analysis, scripting, and CAD import/export. The architecture is a modular monolith separating core computational library (flow5-lib), I/O serialization (flow5-io-lib), and the Qt application (flow5-app) with three main modules: XDirect (foils), XPlane (aircraft), and XSail (boats/sails). While the codebase shows professional engineering craftsmanship with well-defined abstractions for panel methods, splines, and task threading, it suffers from technical debt including global static state, code duplication between libraries, and experimental/test components intermingled with production code.