  While the origin and composition of dark matter and dark energy remains
unknown, it is possible that they might represent two manifestations of a
single entity, as occurring in unified dark sector models. On the other hand,
advances in our understanding of the dark sector of the Universe might arise
from Cosmic Dawn, the epoch when the first stars formed. In particular, the
first detection of the global 21-cm absorption signal at Cosmic Dawn from the
EDGES experiment opens up a new arena wherein to test models of dark matter and
dark energy. Here, we consider generalized and modified Chaplygin gas models as
candidate unified dark sector models. We first constrain these models against
Cosmic Microwave Background data from the \textit{Planck} satellite, before
exploring how the inclusion of the global 21-cm signal measured by EDGES can
improve limits on the model parameters, finding that the uncertainties on the
parameters of the Chaplygin gas models can be reduced by a factor between $1.5$
and $10$. We also find that within the generalized Chaplygin gas model, the
tension between the CMB and local determinations of the Hubble constant $H_0$
is reduced from $\approx 4\sigma$ to $\approx 1.3\sigma$. In conclusion, we
find that the global 21-cm signal at Cosmic Dawn can provide an extraordinary
window onto the physics of unified dark sectors.
