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
Pidgin is a versatile chat client supporting multiple protocols, making it suitable for users who want a comprehensive messaging solution. In contrast, Psi is specialized for XMPP, offering advanced features for XMPP users but lacks the broader protocol support and customization options of Pidgin.