  We introduce Witworld: a generalised probabilistic theory with strong
post-quantum features, which subsumes Boxworld. Witworld is the first theory
that features post-quantum steering, and also the first that outperforms
quantum theory at the task of remote state preparation. We further show
post-quantum steering to be the source of this advantage, and hence present the
first instance where post-quantum steering is a stronger-than-quantum resource
for information processing.
