Analogue spacetimes, (as opposed to general relativity spacetimes), arise when applying the mathematics of differential geometry to generic physical systems.As long as the perturbations have finite propagation speed, then the causal structure can be summarized by propagation cones, similar to the light cones of general relativity; thereby defining a conformal structure. Often one can go further and define an analogue Lorentzian metric. Sometimes these techniques can be used to gain a clearer understanding of general relativity.Sometimes the logic flows the other way --- and then the tools of general relativity can be used to gain insight into radically different physical systems.