  We document our Fortran 77 code for multicanonical simulations of 4D U(1)
lattice gauge theory in the neighborhood of its phase transition. This includes
programs and routines for canonical simulations using biased Metropolis
heatbath updating and overrelaxation, determination of multicanonical weights
via a Wang-Landau recursion, and multicanonical simulations with fixed weights
supplemented by overrelaxation sweeps. Measurements are performed for the
action, Polyakov loops and some of their structure factors. Many features of
the code transcend the particular application and are expected to be useful for
other lattice gauge theory models as well as for systems in statistical
physics.
