Jitsi (formerly SIP Communicator) is a free and open source multiplatform voice (VoIP), videoconferencing and instant messaging application. Developed by University of Strasbourg (France), plus many others.
License: Open Source
Jitsi and Ring are both open-source video conferencing solutions, but they cater to slightly different audiences. Jitsi focuses on ease of use and quick setup, while Ring emphasizes privacy with its decentralized architecture.