BOOPSI (Basic Object-Oriented Programming System for Intuition) is an object-oriented framework introduced in AmigaOS 2.0 that extends the Intuition GUI toolkit with class-based programming capabilities. It enables developers to create and manipulate GUI elements as objects using a message-passing architecture, despite AmigaOS being implemented in the procedural C language. The system utilizes a class hierarchy with root classes such as GadgetClass and ImageClass, providing the foundation for advanced user interface libraries including MUI and ReAction.