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
WhatsApp Messenger is primarily a messaging app with a strong emphasis on privacy and ease of use, making it ideal for personal communication. In contrast, Jitsi is a more versatile platform focused on video conferencing and collaboration, suitable for larger meetings and events.