  We study a generalization of the Wigner function to arbitrary tuples of
hermitian operators, which is a distribution uniquely characterized by the
property that the marginals for all linear combinations of the given operators
agree with the quantum mechanical distributions. Its role as a joint
quasi-probability distribution is underlined by the property that its support
always lies in the set of expectation value tuples of the operators. We
characterize the set of singularities and positivity, and provide some basic
examples.
