Pidgin is a free and open-source chat client which supports AIM, Google Talk, ICQ, XMPP protocols. Developed by Pidgin
License: Open Source
Apps available for Mac OS X Windows Linux BSD PortableApps.com
Gajim is an instant messaging client for the XMPP protocol which uses the GTK+ toolkit. Developed by Gajim Team
Apps available for Windows Linux BSD Xfce
Pidgin is a versatile multi-protocol instant messaging client suitable for users who require connectivity to various chat networks, while Gajim is a dedicated XMPP client focusing on providing a modern and secure experience for XMPP users.