  In low-mass binary systems, mass transfer is likely to occur via a slow and
dense stellar wind when one of the stars is in the AGB phase. Observations show
that many binaries that have undergone AGB mass transfer have orbital periods
of 1-10 yr, at odds with the predictions of binary population synthesis models.
We investigate the mass-accretion efficiency and angular-momentum loss via wind
mass transfer in AGB binary systems. We use these quantities to predict the
evolution of the orbit. We perform 3D hydrodynamical simulations of the stellar
wind lost by an AGB star using the AMUSE framework. We approximate the thermal
evolution of the gas by imposing a simple effective cooling balance and we vary
the orbital separation and the velocity of the stellar wind. We find that for
wind velocities $v_{\infty}$ larger than the relative orbital velocity of the
system $v_\mathrm{orb}$ the flow is described by the Bondi-Hoyle-Lyttleton
approximation and the angular-momentum loss is modest, leading to an expansion
of the orbit. For low wind velocities an accretion disk is formed around the
companion and the accretion efficiency as well as the angular-momentum loss are
enhanced, implying that the orbit will shrink. We find that the transfer of
angular momentum from the orbit to the outflowing gas occurs within a few
orbital separations from the center of mass of the binary. Our results suggest
that the orbital evolution of AGB binaries can be predicted as a function of
the ratio $v_{\infty}/v_\mathrm{orb}$. Our results can provide insight into the
puzzling orbital periods of post-AGB binaries and suggest that the number of
stars entering into the common-envelope phase will increase. The latter can
have significant implications for the expected formation rates of the end
products of low-mass binary evolution, such as cataclysmic binaries, type Ia
supernova and double white-dwarf mergers. [ABRIDGED]
