Psi is a cross-platform powerful XMPP/Jabber client (Qt, C++) designed for the Jabber power users. Psi+ is a development branch of Psi IM XMPP/Jabber client. Developed by http://psi-plus.com/
License: Open Source
Trillian is a user-friendly, multi-protocol instant messaging client with video calling capabilities and a polished interface, making it ideal for personal use. In contrast, Psi+ is an open-source, highly customizable platform favored by developers and technical users, but it may be less accessible for casual users due to its steeper learning curve and less polished design.