Dark energy from coexistence of phases
  We suggest that the current acceleration of the universe may be explained by the vacuum energy of a hidden sector which is stuck in a state of equilibrium between phases. The phases are associated to a late-time first-order phase transition, where phase coexistence originates at a temperature $T_c \sim 10^{-3}eV$ and lasts until temperature falls below $T\sim 10^{-4}eV$. During phase coexistence, the energy density has an effective cosmological constant component with the observed magnitude. This scenario does not require supercooling and may arise naturally in realistic models. 
Ariel Megevand