  We describe models of nonthermal photon emission from a homogeneous
distribution of relativistic electrons and protons. Contributions from the
synchrotron, inverse Compton, nonthermal bremsstrahlung and neutral-pion decay
processes are computed separately using a common parameterization of the
underlying distribution of nonthermal particles. The models are intended for
use in fitting spectra from multi-wavelength observations and are designed to
be accurate and efficient. Although our applications have focused on Galactic
supernova remnants, the software is modular, making it straightforward to
customize for different applications. In particular, the shapes of the particle
distribution functions and the shape of the seed photon spectrum used by the
inverse Compton model are defined in separate modules and may be customized for
specific applications. We assess the accuracy of these models by using a
recurrence relation and by comparing them with analytic results and with
previous numerical work by other authors.
