The name Pies (pronounced "p-yes") stands for Program Invocation and Execution Supervisor. This utility starts and controls execution of external programs, called components. Each component is a stand-alone program, which is executed in the foreground. Upon startup, pies reads the list of components from its configuration file, starts them, and remains in the background, controlling their execution. If any of the components terminates, the default action of Pies is to restart it. However, it can also be programmed to perform a variety of another actions such as, e.g. sending mail notifications to the system administrator, invoking another external program, etc.

GNU pies can also be used as init daemon — the first process started during booting. The configuration can be supplied both as a traditional /etc/inittab file or as a native GNU pies configuration file, which gives much more flexibility. The control interface provides extensive monitoring and management capabilities.