VisSim is described as '™ is a visual language for modeling and simulating nonlinear dynamic systems. With 9 integration methods, 4 optimization methods and over 200 vector and scalar block functions'. There are more than 10 alternatives to VisSim for a variety of platforms, including Windows, Linux, Mac, Online / Web-based and Android. The best alternative is GNU Octave, which is both free and Open Source. Other great apps like VisSim are MATLAB (Paid), Mathematica (Paid), Scilab (Free, Open Source) and SageMath (Free, Open Source).
Octave is a computer program for performing numerical computations which is mostly compatible with MATLAB. It is part of the GNU Project. It is free software under the terms of the GNU General Public License.
MATLAB is a numerical computing environment and programming language. Maintained by The MathWorks, MATLAB allows easy matrix manipulation, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs in other languages.
SageMath is a free open-source mathematics software system licensed under the GPL. It builds on top of many existing open-source packages: NumPy, SciPy, matplotlib, Sympy, Maxima, GAP, FLINT, R and many more.
Maxima is a system for the manipulation of symbolic and numerical expressions, including differentiation, integration, Taylor series, Laplace transforms, ordinary differential equations, systems of linear equations, polynomials, and sets, lists, vectors, matrices, and tensors.
wxMaxima is a document based interface for the computer algebra system Maxima. wxMaxima uses wxWidgets and runs natively on Windows, X11 and Mac OS X. wxMaxima provides menus and dialogs for many common maxima commands, autocompletion, inline plots and simple animations.