About.com Chatting Topic
Take a look at the excellent links on chatting from the
chatting guide.
GTKYahoo
This is a Yahoo! Pager compatible program for Unix.
ICQ
ICQ is AOL's extremely popular messaging system for letting people
communicate with their friends online. Download available free.
IRCHelp
Information about Internet Relay Chat (IRC) programs, including
links to free program downloads.
MSN Messenger Service
Microsoft's Messenger program. Download it free here.
Net Messaging Called 'Catastrophic'
An excellent article from Wired about the poor security in ICQ.
Online Turf Battle Flares
A good article about AOL's anti-consumer tactics with AOL in
preventing other messaging programs from interoperating.
Yahoo! Messenger
Download the Yahoo! Messenger here, for free.
ICQ Developer's Zone
Information for developers about using ICQ's APIs and how to link
external applications to ICQ.
ICQ Hacking Site
ICQ Protocol specification and links to source code for ICQ-compatible
clients.
ICQ Protocol Page
Information about ICQ's protocol and links to ICQ compatible clients
on various operating systems (such as Linux, BeOS, OS/2, and more).
ICQ So-Called Protocol
This page describes and shows the security vulnerabilities of an
older version the ICQ protocol.
Internet Messaging and Presence Protocol (IMPP)
This is a new standard for Internet messaging and chat programs,
supported by the IETF.
Yahoo! Pager Security Problem
A message describing some security concerns about the Yahoo! Pager
protocol.
Elsewhere on About.com 
