  We present a joint optical/X-ray analysis of the massive galaxy cluster Abell
2744 (z=0.308). Our strong- and weak-lensing analysis within the central region
of the cluster, i.e., at R<1Mpc from the brightest cluster galaxy, reveals
eight substructures, including the main core. All of these dark-matter halos
are detected with a significance of at least 5sigma and feature masses ranging
from 0.5 to 1.4x10^{14}Msun within R<150kpc. Merten et al. (2011) and
Medezinski et al. (2016) substructures are also detected by us. We measure a
slightly higher mass for the main core component than reported previously and
attribute the discrepancy to the inclusion of our tightly constrained
strong-lensing mass model built on Hubble Frontier Fields data. X-ray data
obtained by XMM-Newton reveal four remnant cores, one of them a new detection,
and three shocks. Unlike Merten et al. (2011), we find all cores to have both
dark and luminous counterparts. A comparison with clusters of similar mass in
the MXXL simulations yields no objects with as many massive substructures as
observed in Abell 2744, confirming that Abell 2744 is an extreme system. We
stress that these properties still do not constitute a challenge to
$\Lambda$CDM, as caveats apply to both the simulation and the observations: for
instance, the projected mass measurements from gravitational lensing and the
limited resolution of the sub-haloes finders. We discuss implications of Abell
2744 for the plausibility of different dark-matter candidates and, finally,
measure a new upper limit on the self-interaction cross-section of dark matter
of sigma_{DM}<1.28cm2/g(68\% CL), in good agreement with previous results from
Harvey et al. (2015).
