SAP is a general purpose FEA software package for structural design. You can easily analyze and design most types of steel, concrete and light gage members as well as complex buildings. ETABS is tailor made to design steel and concrete structures. The menus are customized for those applications rather than general structural analysis and design. I use SAP for finite and linear element analysis of continuous steel and concrete beams, retaining walls, simple frames, etc. It is capable of so very much more, but for now that's what I'm using it for. I use ETABS to model, analyze and design steel and concrete buildings. I hope this helps.