JModelica is described as 'Extensible Modelica-based open-source platform for optimization, simulation, and analysis of complex dynamic systems' and is an app. There are more than 10 alternatives to JModelica for a variety of platforms, including Windows, Linux, Mac, Web-based and Chrome OS apps. The best JModelica alternative is Simulink. It's not free, so if you're looking for a free alternative, you could try OpenModelica or SimulationX. Other great apps like JModelica are Wolfram SystemModeler, Scicos, Collimator and Altair Activate.