These 10 multi protocol chat clients are totally Free and many of them support social networking sites like twitter, Facebook, Myspace etc too.
I. Digsby - http://www.digsby.com/
Digsb support AIM, MSN, Yahoo, ICQ, Google Talk, and Jabber and you can use more than one chat account to be logged in at a time. The chat have tabbed interface which is another cool feature. It support themes and you may create your own themes if you want.
Additional features are
1. Email notifications - alerts you of new email and lets you perform actions such as 'Delete' or 'Report Spam' with just one click.
2. Social Networking - digsby will allow you to manage your Twitter and Facebook MySpace and LinkedIn accounts.
3. you need not to enter the details every time you use (even it is on another machine), the digsby account login will bring all the required details.
4. You can use a digsby widget in your website which will enable your visitors to chat with you.
More features - http://www.digsby.com/features.php
Digsby is available for Windows only as of now.
II. Pidgin - http://www.pidgin.im/
Pidgin is a free multi protocol chat client (no ads too), and Pidgin runs on Windows, Linux, and other UNIX operating systems. It supports tabbed chat window
Supported chat networks:
Zephyr, Yahoo, XMPP, Sametime, SIMPLE, SILC, QQ, MySpaceIM, MSN, IRC, ICQ, Groupwise, Google Talk (Gtalk), Gadu-Gadu, Bonjour, AIM
It supports plugins which will help you to perform aditional functions. Read more about pidgin plugins Here - http://developer.pidgin.im/wiki/ThirdPartyPlugins
III. Trillian Basic - http://www.trillian-messenger.net/
trillian is also a multi protocol chat client. It have two versions which is Basic (Free) and Pro(not free). It supports ICQ, AIM, Yahoo Messenger, MSN, and IRC. Trillian is also skinnable. It is have an option to get a web based chat client too check it here - http://www.trillian.im/.
Read more about the trillian web here - http://www.trillian.im/learn/tour-web.html
you can get an iPhone app of trillian here - http://www.trillian.im/learn/tour-iphone.html?a=6
Trillian is currently available for windows only.
More screen shots - http://www.trillian.im/learn/screenshots/#more
IV. Instantbird - http://www.instantbird.com/
Instantbird is a free multi protocol chat client which you can use to chat on all famous chat networks, like AIM, MSN, Yahoo, Google, ICQ, IRC, XMPP, QQ etc. The latest beta version supports tabbed chat window
Instantbird supports Windows, MAc and Linux
V. Ayttm - http://ayttm.sourceforge.net/
Ayttm is a free multi protocol chat client which supports protocols such as MSN, Yahoo, AIM, Jabber, and more. Ayttm is developed primarily for Linux but it is also available on BSD and Windows NT/2000 platforms. Windows installation file here - http://sourceforge.net/projects/ayttm/
It supports Tabbed chat, with color alerts for new messages.
VI. Nimbus - http://www.nimbuzz.com/en/pc/
By using Nimbus with one secure log-in (Nimbus username and password) you can access Windows Live Messenger (MSN), Yahoo, ICQ, AIM, Google Talk, Facebook, MySpace, Gadu-Gadu, Hyves and many more. You can call you friends for free.
It supports Mac and Windows
You can get a mobile version of nimbus here - http://www.nimbuzz.com/en/mobile/
You can try a webchat and more info here - http://www.nimbuzz.com/en/web/
VII. Miranda IM - http://www.miranda-im.org/
Miranda IM is a free multi-protocol instant messaging client for Windows. It supports AIM, Facebook, Gadu-Gadu, IAX, ICQ, IRC, Jabber, MSN, Netsend, Tlen, Yahoo, And more. It is customizable
It supports addons which will provide you additional features, more here - http://addons.miranda-im.org/
VIII. qnext - http://www.qnext.com/
Qnext is a free multi-protocol chat client (it is more than a chat client)which will allow you to communicate with your friends on MSN, ICQ, Yahoo, AIM, iChat, GoogleTalk, IRC, and Jabber. It is available for Mac, Windows and Linux
It supports live Video conference with up to 4 people or Voice conference with up to 8 people.
The file sharing and photo sharing services are easier to use (Drag and drop any file or folder at any size onto any Qnext user. Your Qnext contact will receive your file over SSL encryption).
You can stream your music files - http://www.qnext.com/music_streaming.shtml
Instant games - http://www.qnext.com/online_gaming.shtml
Remote PC Access - Qnext MyPC is a Remote Access and Application Sharing service included in Qnext. Basically, it lets you give yourself or anyone you specify access to your computer or specific applications from any standard web browser - https://www.qnext.com/mypc.php
IX. qutIM - http://www.qutim.org/
qutIm is a free open source multiprotocol chat client which will support ICQ, Jabber/GTalk/Ya.Online/LiveJournal.com, Mail.Ru, IRC. This is available for Windows and linux Operating systems.
You can change the look and feel of the application by getting themes and extensions from http://www.qutim.org/look-n-feel
X. yoono (in Beta) - http://www.yoono.com/
Yoono is a cool free appliocation that will be very much a handy one if you are a user of social media applications like Twitter, Facebook, MySpace, FriendFeed etc. It supports Gtalk, MSn, Yahoo instant messaging too. You can use Yoono as a browser add-on, an installed application or as a portable application.
This is having many features like
1. Update status on all networks
2. Easy sharing of images and videos on all networks
3. Column mode to see the updates of diffrent services in diffrent columns at a time
4. This supports tabbed chatting too
5. You can share Text, Image or video from a page which you are visting with your friends
This application is available for Mac, Windows and Linux
Yoono is an easy to use application that allows you to connect to all your social networks and instant messaging services - in one place. Get all your friend updates, update your own status, and easily share stuff with your friends.