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 is ideal for large group video conferencing and offers seamless browser integration, while Linphone is better suited for high-quality audio and video calls with strong privacy features. Both are open-source, but their core functionalities cater to different user needs.