Abstract. We introduce a user-empowered UDP packet reflector to create virtual multicasting environments as an overlay on top of current unicast networks. The end-users’ ability to fully control this environment by a specific communication protocol is the main advantage of our approach. Serializing the parallel communication schema for group communication allows us to introduce special features that are possible in unicast communication only. Similar to working with programmable routers, users can submit their own modules, which can be linked into the reflector and perform user-specific operations (filtering, transcoding etc.). The reflector is the basic element of the overlay network support for the user-empowered group communication in collaborative environments.