1. A system adapted to generate a modified application data structure for modeling physical systems, the modified application data structure being generated from guided user inputs received through one or more application builder wizard graphical user interfaces, the system comprising: one or more modeling system processing units, one or more user input devices, optionally a display device, and one or more memory devices, the one or more modeling processing units being adapted, during use, to embed a pre-determined or a user-selected multiphysics model data structure in an initial application data structure, wherein the multiphysics model data structure comprises data representing one or more models of physical systems, each model of a physical system representing physical phenomena and/or physical processes, the multiphysics model data structure further comprising data representing at least one modeling operation for determining how to model or simulate the one or more models of physical systems, define one or more new window forms, in response to defining the one or more new window forms, add window form data representing the defined one or more new window forms to the initial application data structure, receive one or more selections for application features from one or more user-selectable application feature options displayed in one or more of the application builder wizard graphical user interfaces, and in response to receiving the one or more selections, add application feature data corresponding to the received one or more selections, the application feature data representing one or more application features for the one or more new window forms, the application feature data being added to the initial application data structure to create a modified application data structure that further includes the window form data, each added application feature comprising one or more of (i) first data representing at least one widget included in at least one of the new window forms, (ii) second data representing at least one form feature included in at least one of the new window forms, and/or (iii) third data representing at least one command sequence initiated through the at least one widget included in at least one new window form, wherein the at least one form feature comprises one or more fields for specifying input data and/or output data and/or presentation format of input and/or output data, and wherein a command sequence comprises data specifying a sequence of operations to be carried out when executing an application defined by the modified application data structure, and wherein the at least one widget is linked to the command sequence such that selection of the at least one widget, during execution of the application, is operable to initiate the command sequence, the command sequence including execution of at least one operation for the one or more models of physical systems defined in the embedded multiphysics model data structure, whereby a modified application data structure is generated and stored in the one or more memory devices, the generated modified application data structure providing, when executed, a customized modeling of the physical systems in response to customized user inputs received via the one or more new window forms and the one or more application features for the one or more new window forms.