  In the past decade IceCube's observations have revealed a flux of
astrophysical neutrinos extending to $10^{7}~\rm{GeV}$. The forthcoming
generation of neutrino observatories promises to grant further insight into the
high-energy neutrino sky, with sensitivity reaching energies up to
$10^{12}~\rm{GeV}$. At such high energies, a new set of effects becomes
relevant, which was not accounted for in the last generation of neutrino
propagation software. Thus, it is important to develop new simulations which
efficiently and accurately model lepton behavior at this scale. We present
TauRunner a PYTHON-based package that propagates neutral and charged leptons.
TauRunner supports propagation between $10~\rm{GeV}$ and $10^{12}~\rm{GeV}$.
The package accounts for all relevant secondary neutrinos produced in
charged-current tau neutrino interactions. Additionally, tau energy losses of
taus produced in neutrino interactions is taken into account, and treated
stochastically. Finally, TauRunner is broadly adaptable to divers experimental
setups, allowing for user-specified trajectories and propagation media,
neutrino cross sections, and initial spectra.
