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 a versatile open-source platform primarily focused on video conferencing and collaborative features, while Zoiper is a robust VoIP client that excels in audio and video calls across various protocols. Jitsi is more suitable for group meetings, while Zoiper caters to individual users and businesses needing reliable VoIP communication.