PROPOSAL (Propagator with optimal precision and optimized speed for all
leptons) is presented as a public tool for propagating leptons and gamma rays
through media. Up-to-date cross sections for ionization, bremsstrahlung,
photonuclear interactions, electron pair production, Landau–Pomeranchuk–Migdal
and Ter-Mikaelian effects, muon and tau decay, as well as Molière scattering
are implemented for different parametrizations.