I have a CFD (computational fluid dynamics) grid generation program. It has about 50 windows and over a thousand PUI (Picoscopic User Interface--part of Steve Baker's other project) widgets. It allows the user to define and manipulate points, vectors (directions), lines straight and curved, surfaces flat and curved, and grids of different shapes and sizes.
I support Windows, Linux, and SGI Unix because my customers run on those platforms.
John F. Fay