They're using different representations for solid geometry. ImplicitCAD is using implicit surfaces / functional representations, while OpenSCAD is using a boun

They're using different representations for solid geometry. ImplicitCAD is using implicit surfaces / functional representations, while OpenSCAD is using a boundary representation (which is a lot more common in commercial packages). Implicit surfaces are a very nice representation and make certain operations very easy: booleans become MIN or MAX functions between two functions. However, it becomes much harder to do feature-based operations -- a task like "bevel that edge" is tricky when the edge is an emergent property of the function, rather than as part of the model's explicit representation.