Programmers of large-scale trusted systems need tools to simplify tasks such as replicating services or data. Group communication systems achieve this via various flavors of reliable multicast, but the existing solutions do not scale in all major dimensions. Typically, they scale poorly in the number of groups; yet we believe that using groups casually could lead to new, easier ways of programming. We propose QSM [1], a new multicast substrate that scales in several dimensions at once. Our approach relies on a novel way of exploiting the overlap between groups.