A Measure Algebra which has many properties associated with the convolution Measure Algebra of a Group, but no algebraic structure is assumed for the underlying Space.
References
Bloom, W. R.; and Heyer, H. The Harmonic Analysis of Probability Measures on Hypergroups.
Berlin: de Gruyter, 1995.
Jewett, R. I. ``Spaces with an Abstract Convolution of Measures.'' Adv. Math. 18, 1-101, 1975.