20-sim is described as 'Is commercial modeling and simulation program for multidomain dynamic systems, which is developed by Controllab. With 20-sim models can be entered as equations, block diagrams, bond graphs and physical components' and is an app. There are more than 10 alternatives to 20-sim for a variety of platforms, including Windows, Linux, Mac, Web-based and Chrome OS apps. The best 20-sim alternative is Simulink. It's not free, so if you're looking for a free alternative, you could try Xcos or OpenModelica. Other great apps like 20-sim are PyDSTool, Wolfram SystemModeler, JModelica and Dymola.