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 and collaboration, making it ideal for online meetings, while Trillian is a multi-protocol instant messaging application with a strong emphasis on secure messaging and file sharing. Both have their unique strengths, with Jitsi being open-source and customizable, and Trillian offering cross-platform support and encryption.