  We propose and characterize a new $\mathbb{Z}_2$ class of topological
semimetals with a vanishing spin--orbit interaction. The proposed topological
semimetals are characterized by the presence of bulk one-dimensional (1D) Dirac
Line Nodes (DLNs) and two-dimensional (2D) nearly-flat surface states,
protected by inversion and time--reversal symmetries. We develop the
$\mathbb{Z}_2$ invariants dictating the presence of DLNs based on parity
eigenvalues at the parity--invariant points in reciprocal space. Moreover,
using first-principles calculations, we predict DLNs to occur in Cu$_3$N near
the Fermi energy by doping non-magnetic transition metal atoms, such as Zn and
Pd, with the 2D surface states emerging in the projected interior of the DLNs.
This paper includes a brief discussion of the effects of spin--orbit
interactions and symmetry-breaking as well as comments on experimental
implications.
