We introduce a notion of
“hopfish algebra” structure on an associative algebra, allowing the structure
morphisms (coproduct, counit, antipode) to be bimodules rather than algebra
homomorphisms. We prove that quasi-Hopf algebras are hopfish algebras. We find
that a hopfish structure on the algebra of functions on a finite set G is closely related
to a “hypergroupoid” structure on G. The Morita theory of hopfish algebras is also
discussed.