Geant4 is a toolkit for the simulation of the passage of particles through matter.
Its areas of application include high energy, nuclear, and accelerator physics, as well as studies in medical and space science.
Updated on Jul 08 2022
Note: there are pre-compiled packages of Geant4, but it's recommended to download source code and compile it by yourself to get 100% functionality.
Full list of release notes is available here.