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
Signal is primarily a secure messaging app with a focus on privacy and end-to-end encryption, while Jitsi is an open-source platform designed for video conferencing and collaboration. Signal excels in personal messaging and security features, whereas Jitsi provides robust support for group video calls and screen sharing.