Modeling in SNT is performed through Cortex3D (Cx3D) and sciview. Cx3D was developed in 2009 as a computational modeling tool for simulating neurodevelopmental processes and is well known for generative models of cortical circuits. The Morphonets distribution of Cx3D was modified by Kyle Harrington to be compatible with SNT and the ImageJ ecosystem. This includes using sciview for 3D visualization, and support for image-based modeling.
Currently, an IDE is the most effective way to implement custom models, using the minimal-cx3d-example-project as a template. For more information refer to the GitHub project page.