Prior to writing about the Discworld, Terry Pratchett wrote about the worlds of Strata, and Carpet People and later the Bromeliad Trilogy (Truckers, Diggers, Wings).
These settings have not seen as much love and attention as the Discworld, but has anyone extended these universes into other novels or stories?
I'm thinking in a similar way that the Cthulhu mythos has grown over the years.