This package consolidates the disparate formats of neutrino beam simulation "flux" files.
There is code to define the ROOT TTree format, assist in filling it in the beam simulations, and an interface to GENIE.
These "flux" files encapsulate information about the hadron or muon decay the gave rise to a neutrino. Using the particulars allows the re-evaluation the probability (and energy) of the neutrino ray passing through any arbitrary point.
There were at least 5 precursor variants [gnumi (geant3-based), g4numi, g4numi-minerva, flugg, g4lbne] with many similar elements but also different additions and formatting (both of element type and naming, mostly capitalization).