Accessible software can be used by the widest range of people including those with limited visual acuity, hearing difficulties, color blindness, motor control issues, and other factors that limit their ability to interact with the software using all the elements on the user interface.
Stella, by its nature, is very difficult to use for people with vision or motor issues because it relies on the visual representation of model structure in the creation of the model. Interfaces built using Stella models can, however, be made more accessible.
Much of the accessibility of an interface is determined by basic design. For example, although storytelling is a very powerful way of communicating the relationship between structure and behavior, it does nothing for people who can't see the structure unfold. Presenting summary outcome measures with text descriptions instead will make your interface much more generally accessible.
When creating the interface stick primarily to numeric displays and tables as the output mechanism, and numeric input (or group input) as the input mechanism. Sounds can be helpful.
To be accessible, it is important that an interface can be controlled without a mouse. This means that every object on the interface should have a tab order (so the user can move between controls) and alternative text, so that the use can use a screen reader to determine what the control is. Note that outputs such as the numeric display need to be reachable in this way for the user to learn their content.
Every objects (even ones you will likely not use) can have a tab order and alternative text set. To enable this go to the Publishing Options dialog and select the option to make the interface screen reader friendly.
Once you have done this, everything in the interface will have an accessibility option on the Styles Tab. Use this to set up the way that the tab key will navigate through the interface and the text that will be read during this navigation.