In this paper we describe a novel Model-View-Controller based architecture, Centralized Control, that introduces collaboration in single-users applications. The architecture is able to add collaboration with no need to modify the source code of the original single-user application, and providing also the capability to introduce group semantics into the new, collaborative application that is obtained. The architecture is shown in practice, by introducing CollabXMind, a collaborative mind map tool, that is based on a well-known single-user tool, XMind.