  Driven-dissipative systems are expected to give rise to non-equilibrium
phenomena that are absent in their equilibrium counterparts. However, phase
transitions in these systems generically exhibit an effectively classical
equilibrium behavior in spite of their non-equilibrium origin. In this paper,
we show that multicritical points in such systems lead to a rich and genuinely
non-equilibrium behavior. Specifically, we investigate a driven-dissipative
model of interacting bosons that possesses two distinct phase transitions: one
from a high- to a low-density phase---reminiscent of a liquid-gas
transition---and another to an antiferromagnetic phase. Each phase transition
is described by the Ising universality class characterized by an (emergent or
microscopic) $\mathbb{Z}_2$ symmetry. They, however, coalesce at a
multicritical point, giving rise to a non-equilibrium model of coupled
Ising-like order parameters described by a $\mathbb{Z}_2 \times \mathbb{Z}_2$
symmetry. Using a dynamical renormalization-group approach, we show that a pair
of non-equilibrium fixed points (NEFPs) emerge that govern the long-distance
critical behavior of the system. We elucidate various exotic features of these
NEFPs. In particular, we show that a generic continuous scale invariance at
criticality is reduced to a discrete scale invariance. This further results in
complex-valued critical exponents and spiraling phase boundaries, and it is
also accompanied by a complex Liouvillian gap even close to the phase
transition. As direct evidence of the non-equilibrium nature of the NEFPs, we
show that the fluctuation-dissipation relation is violated at all scales,
leading to an effective temperature that becomes "hotter" and "hotter" at
longer and longer wavelengths. Finally, we argue that this non-equilibrium
behavior can be observed in cavity arrays with cross-Kerr nonlinearities.
