Visualization
The visualization chapter of the Geant4 Book For Application Developers documents in detail how to visualize detector geometries, particle trajectories, and other things using various tools. The following are the ones I use frequently.
You can click the badges above to learn more about individual tools or watch the following tutorial for an overview:
X11 Server for Remote Geant4 Visualization
For people who run visualization programs in a remote Linux machine or a Linux container, an X11 server program is needed for Mac and Windows: