  Accreting black holes are sources of major interest in astronomy, particular
those launching jets because of their ability to accelerate particles, and
dramatically affect their surrounding environment up to very large distances.
The spatial, energy and time scales at which a central active black hole
radiates and impacts its environment depend on its mass. The implied
scale-invariance of accretion/ejection physics between black hole systems of
different central masses has been confirmed by several studies. Therefore,
designing a self-consistent theoretical model that can describe such systems,
regardless of their mass, is of crucial importance to tackle a variety of
astrophysical sources. We present here a new and significantly improved version
of a scale invariant, steady-state, multi-zone jet model, which we rename
bhjet, resulting from the efforts of our group to advance the modelling of
black hole systems. We summarise the model assumptions and basic equations, how
they have evolved over time, and the additional features that we have recently
introduced. These include additional input electron populations, the extension
to cyclotron emission in near-relativistic regime, an improved multiple inverse
Compton scattering method, external photon seeds typical of AGN and a
magnetically-dominated jet dynamical model as opposed to the pressure-driven
jet configuration present in older versions. In this paper, we publicly release
the code on Github and, in order to facilitate the user's approach to its many
possibilities, showcase a few applications as a tutorial.
