Instant Messaging

ActivePager
An instant messenger for local area networks enabling you to talk in real time to anybody on the same computer network. Offers Answering Machine, and Templates and Blacklist.
http://www.reymax.com/active_pager.html

AniazPOPUP
Expands the concept of Windows messaging from the droplet created by winpopup to a new level.
http://www.geocities.com/SiliconValley/Chip/4419/index.html

Bantu
Offers a web-based solution to instant messaging that lets you talk to people with the AOL, MSN, YAHOO, and ICQ messangers.
http://www.bantu.com/

BattleCom
A program that allows you to talk instead of type, a new way of chatting.
http://www.battlecom.fw.nu

BigBlueBall.com
Instant messaging tutorials, reference, news and forums for AIM, MSN, Yahoo, ICQ, Trillian and other products.
http://www.bigblueball.com/

Centericq
A text mode menu and window-driven IM interface that supports the ICQ2000, Yahoo!, AIM, MSN, and IRC protocols and has many other useful features.
http://thekonst.net/centericq

Easy Message
Free all in one instant messenger, including support for MSN Messenger, Yahoo Messenger, AOL Messenger, and ICQ Messenger.
http://www.easymessage.net

EMSN Messenger
EMSN is a PHP-Messaging System.
http://stdio.ch

Endogy
Endogy provides Instant Messaging software and consulting services for the improvement of team workflow.
http://www.endogy.com

FunPidgin
A fork of the pigin IM client, whose developers aims to be more responsive to the views and wishes of users. Project information, feature list, and download.
http://funpidgin.sourceforge.net/

Gtkmsn
A MSN protocol based client. Includes download section and screenshots.
http://gtkmsn.sourceforge.net/

komunikator tlenplus
An extended Tlen client with emotes,skins, and plugins.
http://www.tlenplus.webpl.org

Kopete
Linux based, KDE specific, it is a flexible and extendable multiple protocol instant messenger.
http://kopete.kde.org/

Meca Messenger
Multi protocol Instant messenger with: multimedia integration, skins, SMS capabilities, logs, email viewing and offline messages.
http://www.meca.com/

Miranda Instant Messenger
A modular open-source multi-protocol instant messenger for Windows that maintains a database of community developed plug-in's that add functionality.
http://www.miranda-im.org

OMS Online Messenger Service, SOAP Webservice
A webservice for creating one's own messenger client. Included is a webbased version of OMS.
http://www.myoms.net

OUGO Messenger
A Windows Messenger.
http://www.ougo.com

Pidgin
An instant messaging client, which can handle multiple protocols, including AIM, ICQ, IRC, MSN, Yahoo!, Jabber, and Gadu-Gadu. [Windows, Unix]
http://pidgin.im/

PowWow Messenger
A multi-functional instant messenger program. Including: Chat, Text to Speech engine, games, guestbook, and whitepages.
http://www.jazy.net/powwow/

P2P Messenger .NET
A secure Instant Messaging client, working by Peer-to-Peer technology. It is fully decentralized and does not require any servers. Supports public-key cryptography. Requires installing .NET-Frameworks.
http://www.ufasoft.com/p2p/

Rediff Bol
Allows user to chat, check mail, and search the web.
http://bol.rediff.com/

Trillian
A chat client for Windows that allows you to simultaneously connect to AIM, ICQ, IRC, MSN and Yahoo! Messenger.
http://www.trillian.cc/

VSL LanToucher
Instant messaging software solutions for business and home text communications across private networks.
http://www.vitalsoundlab.com

Winpopup LAN Messenger
A full-featured server-less instant messenger for Local Area Networks.
http://www.winpopup-lan-messenger.com

WinPopup.com
Windows popup messenger. Has the ability to transfer emoticons, and links.
http://www.winpopup.com