  Transverse spin angular momentum is an inherent feature of evanescent waves
which may have applications in nanoscale optomechanics, spintronics, and
quantum information technology due to the robust spin-directional coupling.
Here we analyze a local spin angular momentum density of hybrid surface waves
propagating along anisotropic hyperbolic metasurfaces. We reveal that, in
contrast to bulk plane waves and conventional surface plasmons at isotropic
interfaces, the spin of the hybrid surface waves can be engineered to have an
arbitrary angle with the propagation direction. This property allows to tailor
directivity of surface waves via the magnetic control of the spin projection of
quantum emitters, and it can be useful for optically controlled spin transfer.
