Rings with effects
  A ring with effects (e-ring) is a generalization of the ring of bounded linear operators on a Hilbert space and the subsystem of effect operators (positive Hermitian operators dominated by the identity operator). The POV-measures representing (perhaps fuzzy) quantum mechanical observables take on their valued in the system of Hilbert-space effect operators. We study and give several examples of e-rings, including von Neumann algebras and rings of bounded measurable functions. 
D. J. Foulis