Flitecad

is a specialized, free 2D design tool used primarily for model aircraft (foam or balsa) scratch-building . It is not a full 3D solid modeling software like Fusion 360 or SolidWorks.

Here is the clarification based on typical usage of that software: flitecad

It looks like you're asking about and the concept of a solid piece . is a specialized, free 2D design tool used