20-sim is a modeling and simulation application for dynamic systems. With 20-sim, you can simulate the behavior of dynamic systems, such as electrical, mechanical, and hydraulic ones, or any combination of these systems. The program supports modeling through equations, block diagrams, and bond graphs, allowing you to design and analyze dynamic systems in an intuitive and user-friendly way. It includes a fully observable and unlimited hierarchical model structure\; active support of top-down, inside-out, and bottom-up modeling\; and multiple libraries with a large set of domain-oriented submodels. 20-sim also lets you create your own model icons with its built-in Icon Editor, add graphical elements to models, and use vectors and matrices, as well as multi-dimensional bonds and signals. In addition, the program includes high-performance simulation algorithms, debugging facilities, the ability to export your data and models to Matlab, a built-in runtime compiler to speed up simulations, as well as five toolboxes: parameter optimization, ANSI-C code generation, linearization, graph animation, and 3D animation.