  In this study, we introduce BEoRN (Bubbles during the Epoch of Reionisation
Numerical Simulator), a publicly available Python code that generates
three-dimensional maps of the 21-cm signal from the cosmic dawn and the epoch
of reionisation. Built upon N-body simulation outputs, BEoRN populates haloes
with stars and galaxies based on a flexible source model. It then computes the
evolution of Lyman-$\alpha$ coupling, temperature, and ionisation profiles as a
function of source properties, and paints these profiles around each source
onto a three-dimensional grid. The code consistently deals with the overlap of
ionised bubbles by redistributing photons around the bubble boundaries, thereby
ensuring photon conservation. It accounts for the redshifting of photons and
the source look-back effect for the temperature and Lyman-$\alpha$ coupling
profiles which extend far into the intergalactic medium to scales of order 100
cMpc. We provide a detailed description of the code and compare it to results
from the literature. After validation, we run three different benchmark models
based on a cosmological N-body simulation. All three models agree with current
observations from UV luminosity functions and estimates of the mean ionisation
fraction. Due to different assumptions regarding the small-mass stellar-to-halo
relation, the X-ray flux emission, and the ionising photon escape fraction, the
models produce unique signatures ranging from a cold reionisation with deep
absorption trough to an emission-dominated 21-cm signal, broadly encompassing
the current uncertainties at cosmic dawn. The code BEoRN is publicly available
at https://github.com/cosmic-reionization/BEoRN.

Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies