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 an open-source platform primarily focused on video conferencing with a strong emphasis on privacy and ease of use, while Phoner is more geared towards high-quality audio and video calls with additional messaging features. Both platforms have their strengths, but Jitsi excels in being free and open-source, while Phoner offers robust security and customization.