Perhaps the simplest fully-featured G4 application.
Based on one-file simulation by Jason Detwiler.
Physics List: uses Geant4's named physics lists, set them using macro commands (see example run.mac)
Generator: uses Geant4's GPS. Set it up using macro commands (see example run.mac).
Geometry: uses g4gdml (see example run.mac). Also plan to add a G4tgrLineProcessor-based geometry input scheme.
Output: uses Geant4's analysis manager (root, hdf5, xml, csv), with several configurable options for output format, sensitive volumes, etc (see example run.mac).
Visualization: uses avaialable options in your G4 build (see example vis.mac).
Postprocessing: you will want to postprocess the output to apply the detector response. See example code that runs on the output of run.mac.
See similar project by Jing Liu at https://github.com/jintonic/gears