Psi is a free instant messaging application designed for the XMPP network (including Google Talk). Fast and lightweight, Psi is fully open-source and compatible with Windows, Linux, and Mac OS X.
License: Open Source
Psi is a robust multi-protocol chat client known for its strong encryption and customization options, making it suitable for advanced users. Kopete, on the other hand, offers a more user-friendly experience, particularly for users within the KDE environment, but may lack some advanced features and stability.