Isabel 5.0 release is GPL

Isabel is a multipoint group collaboration tool for performing distributed congresses, classrooms or meetings over the Internet, which uses advanced floor control techniques, TV like production and videoconferencing to achieve an ordered and natural interaction among participants in large multipint configurations. Isabel is intended for group videoconferencing, but it can be used also for the desktop.

You can install it following the instructions at: http://isabel-wiki.dit.upm.es/wiki/Installation