SystoLite is a web page built entriely with Systo widgets. It shows that Systo widgets can be assembled to make a generic modeling environment, one that can work with a range of existing models or in which you can create new models. It is is currently (June 2014) under development, and nearing release.
This screendump shows what the user interface looks like. It has been deliberately designed to not offer too many options, so that the newcomer to System Dynamics modelling is not overwhelmed by a confusing range of choices.
The top half of the screen is for working with the model diagram, while the bottom half is for running simulations. The user can re-size individual panels, by dragging the border, so they have some control over the user interface, but not too much.
To read more about SystoLite and how to use, please have a look at the basic SystoLite guide.