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
CSipSimple is primarily a VoIP solution focused on SIP-based calls, making it ideal for users who need robust voice capabilities. In contrast, Jitsi excels in video conferencing and collaboration, offering a comprehensive set of features for group communication and remote meetings.