Weyl semimetals, three dimensional materials with gapless excitations characterized by an effective Weyl Hamiltonian, are the tree dimensional generalizations of graphene. In connection with the recent rush to find condensed matter realizations of this new phase of matter another equally intriguing novel topological phase has been discovered: nodal line semimetals. In these systems the conduction and valence band touch each other along a line. This line can take a form of a loop or extend trough the whole  Brillouin zone. Systems with many lines entangled with each other were also predicted to exist.