In this paper we present Joyce, a platform and programming framework that enables applications to form the kind of variably-connected, data-sharing group that typifies ubiquitous computing. The platform captures the semantics of application operations via a system of actions and constraints, which it distributes to peers in a group using epidemic propagation. Our system presents several advantages: (1) we capture a rich semantic model of application usage across all participants in a group, (2) we persist this rich semantic model independently of the constituent applications, (3) propagation of the semantic model is tolerant of varying connectivity (4) we use the semantic model to reconcile concurrent modifications from separate participants, (5) we encapsulate all of this functionality in a piece of application-agnostic middleware.