MATLAB has Simulink and Simscape, Maple has MapleSim and Scilab has Xcos. What is the equivalent product for Mathematica?
From the user perspective the conceptual difference between Simulink and SystemModeler is how the analyzed system is described. SystemModeler (WSM) works at the component level while Simulink works at the "block diagram level". This means that the user defines how the components are connected and WSM is responsible for the development and solution of the equations. With Simulink one needs to provide the behavioral description (transfer functions) of each block and the system.