Linked from
The 76 pages that link to Set, each with the reason it gives.
HypergraphRelated: A hyperedge is defined as a subset of the hypergraph’s vertex set.
CategoryRelated: Sets are the objects of the standard category whose morphisms are functions.
Algebraic structureRelated: The elements on which an algebraic structure's operations are defined.
Hom functorRelated: In an arbitrary category, Hom-values are sets rather than necessarily groups.