Here are some chat and messenger applications I have found useful. See also: Chat and Messenger Application Settings, Programs, Operating Systems, Software.
AIM, Google Talk, ICQ, Kopete, Miranda, Pidgin, Psi and Yahoo! Messenger are instant messengers. Colloquy, Ircle, Chatzilla, Irssi, Konversation, Kopete, KSirc, mIRC, and XChat are IRC clients. So, Pidgin and Kopete can be used for both instant messaging and IRC. Colloquy and Ircle are for OS X. Pidgin and XChat are for Linux and Windows platforms. Kopete uses multiple protocols for instant messaging (AIM, Gadu-Gadu, Google Talk, ICQ, Jabber, MSN, Novell GroupWise, WinPopup, Yahoo and with the use of plugins SILC, Skype and SMS). Google Talk can be used for voice conversations. Irssi may already be on your Linux distribution: if you have Ubuntu 7 or later, try typing irssi on a terminal window and follow the possible instructions. SILC Client uses the SILC protocol which is for IRC-like conversations. Windows Ident Server by Rndware helps with authentication when using IRC applications.
Google Talk (no longer available since 2013 or so)
Windows Ident Server by Rndware
Last modified: June 14th, 2014
Author: Tomi Häsä (tomi.hasa@gmail.com)
URL: http://sites.google.com/site/tomihasa/useful-chat-messenger-applications