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 primarily focused on video conferencing capabilities, making it suitable for meetings and webinars, while Riot.im (now known as Element) emphasizes decentralized communication and rich text features, making it ideal for team collaboration. Both are open-source but serve different purposes in the communication landscape.