  Accurate and computationally efficient modeling of systems of interacting
electrons is an outstanding problem in theoretical and computational materials
science. For materials where strong electronic interactions are primarily of a
localized character and act within a subspace of localized quantum states on
separate atomic sites (e.g., in transition metal and rare-earth compounds),
their electronic behaviors are typically described by the Hubbard model and its
extensions. In this work, we describe BoSS (Boson Slave Solver), a software
implementation of the slave-boson method appropriate for describing a variety
of extended Hubbard models, namely $p-d$ models that include both the
interacting atomic sites ("$d$" states) and non-interacting or ligand sites
("$p$" states). We provide a theoretical background, a description of the
equations solved by BoSS, an overview of the algorithms used, the key
input/output and control variables of the software program, and tutorial
examples of its use featuring band renormalization in SrVO$_3$, Ni $3d$
multiplet structure in LaNiO$_3$, and the relation between the formation of
magnetic moments and insulating behavior in SmNiO$_3$. BoSS interfaces directly
with popular electronic structure codes: it can read the output of the
Wannier90 software package which postprocesses results from workhorse
electronic structure software such as Quantum Espresso or VASP.
