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
Screenleap is primarily focused on screen sharing with an easy setup and no downloads, making it ideal for quick presentations. In contrast, Jitsi offers a more comprehensive video conferencing solution with customizable features but requires more technical knowledge to set up.