Google Talk - use GTalk for your voice calls, voice messages, file transfer and Gmail notifications
Skype - high quality calls to anyone, anywhere in the world
Yahoo! Messenger - an official messenger for Yahoo! users, free to use but advertising-supported
AOL Instant Messenger - communicate with AOL registered users via text, voice, and video
Windows Live Messenger - connect and share instantly on the world’s most popular IM network
ICQ - the world’s first instant messaging program
mICQ - a free text-based ICQ client that runs on a wide variety of platforms
Licq - a free clone of the ICQ client for Linux other Unix systems
aMSN - a free and open source MSN Messenger clone for Linux users
JMSN - a pure Java MSN Messenger clone, with many interesting features that MSN doesn’t have
CSpace - secure and peer-to-peer communication to chat or transfer files
Coccinella - a free Jabber/XMPP client with a built-in white board for improved collaboration with other people
Emesene - a MSN Messenger client with a simpler GUI and a nice look
Gajim - a full-featured and easy to use XMPP client for gnome users
GOIM - allows users to chat within DirectX games
mcabber - a small console-based Jabber client that runs on Linux and Mac OS X
Gadu-Gadu - the most popular IM in Poland
Exodus - a Jabber client which is small, fast, easy to use, and looks good
Retroshare - communicate and download files from friends of friends
naim - a console based multi-protocol client with features like peer to peer encryption and module support
Gossip - an instant messaging client for Gnome users, with chat history search
MessageMate - commercial IM platform that provides end-to-end security; interoperable with AIM, ICQ, Yahoo and MSN
Papla Instant - use it on your PC and mobile phone
Mercury Messenger - a full featured Windows Live Messenger client, offers several extra features which are not implemented in MSN
Psi - small, fast Jabber client
Spark - free and open source IM with built-in support for group chat, telephony integration and strong security
Jabbin - free Jabber client that enables free calls using VoIP
YSM - full-featured console-based ICQ client
MySpaceIM - the official instant messaging client for MySpace
OneTeam - IM client is XUL based, so requires Firefox 2
Microsoft Messenger for Mac - the official Mac client for MSN Messenger, but the feature list is limited
Xfire - chat with contacts inside the game, without the need to minimize the game windows
Pandion - Jabber client which supports plugins to extend its features
BitWise IM - a secure, cross-platform client that encrypts all data sent between users
Multi-network IM Clients
Pidgin - most popular, free, multi-platform IM client that supports most of the IM protocols
Miranda IM - lightweight, resource efficient and easy to use client with powerful plugin support
Ayttm - in case of a service failure, this will automatically fall back to other service protocols of the same person you are chatting to.
Trillian - a Windows application that can connect to multiple IM services, with nice features like Metacontact, Instant lookup, and Emotiblips
meetro - find and chat with people nearby, i.e. location-aware client
IMVU - 3D chat which enables you chat in 3D scenes with your own avatars
Kopete - KDE application, provides users with a single, easy-to-use way to access all of their instant messaging systems
MECA - connect to all of your friends on AIM, MSN, Yahoo! and ICQ from just one list
Centericq - text based multi protocols IM client
Proteus - popular client for Mac OS X that supports multiple protocols
Instan-t - Windows client that allows users to communicate with MSN, AIM,
Y!Messenger, ICQ and its IM networks
iChat - IM Client from Apple for Mac OSX
Universal Messenger Plus - a single convenient interface that allows you to easily communicate over different protocols.
Qnext - share your music, photos, and files with anyone, instantly while talking via IM
Aduim - free client for Mac users that can connect to most of the popular messaging services
BitlBee - IRC clients with support of IM protocols
