  We discuss fluctuation-dissipation relations valid under general conditions
even out of equilibrium. The response function is expressed in terms of
unperperturbed correlation functions, where contributions peculiar to
non-equilibrium can appear. Such extra terms take into account the interaction
among the relevant degrees of freedom in the system. We illustrate the general
formalism with two examples: driven granular systems and anomalous diffusion on
comb structures.
