Peter Bubenik and Jonathan Scott, in 2012, made the perspicuous suggestion that any functor, from a suitable source category into any target category, could be regarded as a "generalised persistence module" (GPM), and that categories of GPM carried natural distance functions called interleaving metrics. I will discuss several examples and constructions on GPM. These include Reeb graphs, merge trees, dynamical systems, Morse functions. I will also discuss a recently joint project, led by Anastasios Stefanou and Liz Munch, which extends the interleaving distance from GPM categories to, more generally, categories with a flow.