QQ (South African)
http://www.qq.co.za/
version 1.0
file name: qq.exe
download: 4.76mb
System Requirements:
Windows 95 with Internet Explorer 4 or higher or
Windows 98, 98SE, or ME or
Windows NT4, 2000, or XP
Offers:
Voice and Video, File sharing, Offline messaging, Chat Rooms, SMS's, Message History

Yet Another Messenger
trolling.pwp.blueyonder.co.uk
version 1.84 (25 Sept 05)
file name: YAM-FULL.zip
download: 727kb
as submitted by Stir (thank you :)
"YAM which stands for Yet Another Messenger is a Yahoo! Messenger Replacment and like other 3rd party chat clients for yahoo it protects you against boot codes and spam it has many features like:
Animated Smileys, Animated Avatars, Glyphs - like tattoos exept these are small pictures which u can draw within the program.Voice. Voice in PM, Audibles, Skinnable
Lots more features but the best thing about this client is compared to others it fast everything is instant apart from the pre loading of animated smileys before u login which is to speed up the client and keep the resources down as animation can tend to slow down old win 98 pc's. http://www.trolling.pwp.blueyonder.co.uk/ well worth a look can be a little confusing at first but is pretty easy to figure things out if you need help i wrote the official tutorial on it which can be found at http://ourchat.org/index.php?pid=246"

Paltalk
paltalk.com
Support forum: forums.paltalk.net
Version: 8.0 build 90 (12 May 05)
file name: pal_install_qt_r1215.exe
download: 3.07mb
System Requirements:
Windows 95/98/NT/2000/XP
Microsoft Internet Explorer 5.0+
Offers:
Compatibility with AIM, MSN, Yahoo! and ICQ, Voice and Video, File sharing, Multi-party chat, Offline messaging, Chat Rooms

Eyeball
eyeballchat.com
Version: 2.20.1010.1 (11 October 2002)
file name: ec22.exe
download: 2mb
System Requirements:
An Internet connection
Eyeball Chat software
A free Eyeball ID
Microsoft Windows 98/ME/2000/XP
(they state "A Macintosh and Linux compatible version is being considered for future")
Pentium II 400 Mhz processor with 64 MB of RAM
A full duplex sound card
A headset, or microphone and speakers
A webcam, or video capture device for sending video
Microsoft DirectX 8.0 or later
Offers:
Video/Webcam Voice Chat, Video Messages, support for AIM, MSN & Yahoo! Messengers, Mail Notification for MSN & Yahoo, File Transfer, Eyeball Chat Rooms

Miranda
miranda-im.org
Community forums: forums.miranda-im.org
Version: 0.4
Installer - miranda-im-v0.4.exe (994 KB)
Zip Compression - miranda-im-v0.4.zip (977 KB)
System Requirements:
Windows 95, 98, Me, NT4, 2000 & XP
Offers:
Compatibility with ICQ, AIM, MSN, Jabber, Yahoo!, Gadu-Gadu, Tlen, Netsend, and more
444 plugins (and growing) which offering a huge variety of features
Doesn't need to be installed, can be run from a floppy
Miranda IM is published under the GPL license, free, no ads

Easy Message Express
easymessage.net
version: 2.3.663 (27 June 2004)
file name: setup.exe
download size: 251kb
Offers:
Compatibility with MSN, AIM, ICQ, and Yahoo!
File Transfer
Group Chat
POP3 mail notifications
Really small download (251kb), can be stored easily on a floppy

Instan-t Messenger
interactiveni.com/imsite/imfreeware.htm
Offers:
Basic Instant Messaging
Instant Messages with support for offline messages, File Transfer, Multi-person Chat, History of Messages (stored on the user’s computer), Contact list management with support for multiple folders, Authorization request and hide email privacy settings, User profile, directory and search, Multiple connection states (busy, invisible, etc.)
Advanced Features
Customizable Automatic Replies, Invite by email tool, Email Signature, Web Communication Center, Voice Chat, Video Chat
Interoperability with MSN, AIM, Yahoo!, and ICQ
Instant Messages, File Transfer (Send Files only), Multiperson Multinetwork Chat, Contact list management with support for multiple folders, Voice Chat, Video Chat, Audio Emoticons
Download ~ http://inidownload.com/it/Download/Completo/ITsetup.exe
Support ~ http://www.interactiveni.com/imtechsupport.htm?tech=free

imvite messenger (beta)
imvite.com
System requirements:
Windows: Pentium processor running Windows 98/ME, WinNT4/2000/XP
256MB RAM
30MB of free hard drive space
56k modem or broadband Internet connection
800x600 resolution, 256 colors or more
Full duplex sound card for sound features
Internet Explorer v.5.5 or newer
Offers:
interoperability with MSN, AIM, Yahoo!, and ICQ
file transfer, shopping carts, google search, news headlines, advertising banners, affiliate program
Terms of Use -
http://www.imvite.com/Terms.php
Privacy Policy -
http://www.imvite.com/Privacy_Policy.php

it seems they are no more...

Odigo
odigo.org
Version: 4.0
download: 2.88mb
file name: odigo40_689eng.exe
System Requirements:
Browser Support
IE 4+
Netscape 4.x
NeoPlanet 2.x and 5.x (special plug-in required)
Pentium 100 and up
Minimum 16 MB RAM
Windows 95/98/2000/ME/XP, NT4.0
Offers:
Chat, Intentions, Moods
a challenge getting their site to load...