  Violating the strong constraint of double field theory, non-geometric fluxes
were argued to give rise to noncommutative/nonassociative structures. We derive
in a rather pedestrian physicist way a differential geometry on the simplest
nonassociative (phase-)space arising for a constant non-geometric R-flux. This
provides a complementary presentation to the quasi-Hopf representation
categorial one delivered by Barnes, Schenkel, Szabo in
arXiv:1409.6331+1507.02792. As there, the notions of tensors, covariant
derivative, torsion and curvature find a star-generalization. We continue the
construction with the introduction of a star-metric and its star-inverse where,
due to the nonassociativity, we encounter major deviations from the familiar
structure. Comments on the Levi-Civita connection, a star-Einstein-Hilbert
action and the relation to string theory are included, as well.
