  Noncollinear antiferromagnets, such as Mn$_3$Sn and Mn$_3$Ir, were recently
shown to be analogous to ferromagnets in that they have a large anomalous Hall
effect. Here we show that these materials are similar to ferromagnets in
another aspect: the charge current in these materials is spin-polarized. In
addition, we show that the same mechanism that leads to the spin-polarized
current also leads to a transverse spin current, which has a distinct symmetry
and origin from the conventional spin Hall effect. We illustrate the existence
of the spin-polarized current and the transverse spin current by performing
\emph{ab initio} microscopic calculations and by analyzing the symmetry. We
discuss possible applications of these novel spin currents, such as an
antiferromagnetic metallic or tunneling junction.
