The Sims runs on top of a custom virtual machine and development environment called Edith. As Kenneth Forbus and Will Wright explain in their notes on programming Sims objects, “The Sims’ world is created on top of Edith, which provides a virtual machine plus a development environment for that virtual machine,” and “shipping versions of The Sims have the virtual machine but not the development environment.”
Object behaviors in The Sims are not written in conventional code but as “trees” in a visual programming language, where “statements are represented by boxes” and arrows show flow of control, with green marking the entry point and T/F tabs marking success or failure branches. Forbus, a Northwestern University AI researcher, notes the language was meant “to make it easier for content developers to create objects, and perhaps someday support end-user programming” - an early gesture toward letting non-programmers author game logic visually.