  Dineutrino modes offer promising searches for new physics. The potential
aspects of these modes are reviewed in detail. Performing a proper combination
of them, novel tests of the SM symmetries are derived. Different
phenomenological applications are worked out, including charm, beauty and
kaons, which result in novel tests of lepton universality and charged lepton
flavour conservation with flavour-summed dineutrino observables, in addition to
improved bounds on $\tau\,\ell$ couplings with $\ell=e,\mu,\tau$.
