GSTAR is a framework to run STAR detector simulation using GEANT. This  simulation program is an enhanced version of the interactive GEANT.

As a framework, it

Experiment specific description procedures to read event generator information, detector geometries, new particles properties and decays, definition of hits (signals produced by particles in sensitive detector elements), are external procedure. They may be written as a user code, compiled into shared libraries, and loaded in the framework for execution.