The ATLAS detector simulation is a Geant 4 application: the Geant 4 collaboration web site gives an indication of the institutes involved, latest news and a picture gallery.
Other links :
- This introduction to Simulating physics and detectors is targeted to summer students, and covers applications within and beyond HEP. It was given by a member of the Geant 4 collaboration in the context of the 2014 OPENLAB program.
- A global view is on Wikipedia : http://en.wikipedia.org/wiki/Geant4
- A CERN technology transfer poster : http://geant4.web.cern.ch/geant4/gallery/fullsize/geant4-poster.pdf