We present the software architecture of FMIGo!, a distributed environment for executing Functional Mockup Interface (FMI) based simulations, describe how to use it, and how to extend its functionality. FMI is a standard used to define what different Functional Mockup Units -- or modules -- can expose in terms of inputs and outputs, and the proper execution or call sequence on can perform on said. The FMI does not define the mathematics of modular time integration, a problem addressed by FMIGo! in an extensible way.

Also included are some theoretical and experimental aspects of different stepping schemes, or numerical methods to simulate coupled, modular systems. In particular, we present a kinematic coupling schemes which corresponds to Differential Algebraic Conditions between modules, as well as wrapper FMUs designed to augment the functionality of a given FMU with, for instance, input and output filters and directional derivatives, features rarely present in modules.