If you are looking for tools to design physical balsa planes rather than virtual ones, the following software is commonly recommended by the hobbyist community:

: Users can build detailed aircraft from scratch, adjusting wing geometry, fuselage shapes, and internal components.

: Most Balsa or flight sim mods are placed in a specific "Addons" or "Community" folder. For MSFS, dion73 notes that some airports or utilities may need to be imported individually to register correctly. Related Modeling Software