  Simple but flexible dynamical models are useful for many purposes, including
serving as the starting point for more complex models or numerical simulations
of galaxies, clusters, or dark matter haloes. We present SpheCow, a new
light-weight and flexible code that allows one to easily explore the structure
and dynamics of any spherical model. Assuming an isotropic or Osipkov-Merritt
anisotropic orbital structure, the code can automatically calculate the
dynamical properties of any model with either an analytical density profile or
an analytical surface density profile as starting point. We have extensively
validated SpheCow using a combination of comparisons to analytical and
high-precision numerical calculations, as well as the calculation of inverse
formulae. SpheCow contains readily usable implementations for many standard
models, including the Plummer, Hernquist, NFW, Einasto, S\'ersic, and Nuker
models. The code is publicly available as a set of C++ routines and as a Python
module, and it is designed to be easily extendable, in the sense that new
models can be added in a straightforward way. We demonstrate this by adding two
new families of models in which either the density slope or the surface density
slope is described by an algebraic sigmoid function. We advocate the use of the
SpheCow code to investigate the full dynamical structure for models for which
the distribution function cannot be expressed analytically and to explore a
much wider range of models than is possible using analytical models alone.
