The aim of this paper is to briefly present the general concept of virtual worlds and then to focus on distributed and decentralized ones. MaDViWorld is a Java framework for massively distributed virtual worlds. We first present its software architecture and then discuss some of its specialized features, namely: the object structure and the distributed event model. These are the main aspects that evolved since the first version of the framework. To conclude, some example objects and further potentialities of the framework are discussed.