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
Dialog Messenger is primarily focused on secure messaging and file sharing with robust privacy, making it ideal for personal and small team communication. In contrast, Jitsi excels in video conferencing and collaboration tools, suitable for larger meetings and open-source projects.