GEARS - a Geant4 Example Application with Rich features and Small footprints

We'd like to introduce GEARS, a Geant4 Example Application with Rich features yet Small footprint. The entire C++ coding is minimized down to a single file with about 600 SLOC. This is achieved mainly by utilizing Geant4 plain text geometry description, build-in UI commands (macros), C++ inheritance, and unconventional uses of some standard Geant4 functionalities. It is ideal for student training and fast implementation of small to medium-sized experiments.