  We study the ground state energy of a gas of 1D bosons with density $\rho$,
interacting through a general, repulsive 2-body potential with scattering
length $a$, in the dilute limit $\rho |a|\ll1$. The first terms in the
expansion of the thermodynamic energy density are $\pi^2\rho^3/3(1+2\rho a)$,
where the leading order is the 1D free Fermi gas. This result covers the
Tonks-Girardeau limit of the Lieb-Liniger model as a special case, but given
the possibility that $a>0$, it also applies to potentials that differ
significantly from a delta function. We include extensions to spinless fermions
and 1D anyonic symmetries, and discuss an application to confined 3D gases.
