Multi protocol instant messaging clients

Multi protocol instant messaging software allows users to connect to different IM networks through a single software, which eliminates the use of installing different IM clients for different networks such as Yahoo,MSN, AOL, ICQ, GTalk, and Jabber and also the space required to install different softwares.

Gaim
Operating System: Linux, BSD, MacOS X, and Windows
Supported IM networks: AIM and ICQ (Oscar protocol), MSN Messenger, Yahoo!, IRC, Jabber, Gadu-Gadu, SILC, Novell GroupWise Messenger, Lotus Sametime, and Zephyr networks.
Website: http://gaim.sourceforge.net/

Miranda
Operating System: Windows
Supported IM networks: ICQ, AIM, MSN, Jabber, Yahoo, IRC, Gadu-Gadu, Tlen, Netsend
Website: http://www.miranda-im.org/

Psi
Operating System: Windows, Apple Mac OS X and GNU/Linux
Supported IM networks: AIM, ICQ, MSN, Yahoo, and IRC.
Website: http://psi.affinix.com/home

Trillian
Operating System: Windows
Supported IM networks: AIM, ICQ, MSN, Yahoo Messenger, and IRC
Website: http://www.ceruleanstudios.com/learn/

Instant-T
Operating System: Windows
Supported IM networks: MSN, AOL, Yahoo, ICQ, and Instant-T
Website: http://www.interactiveni.com/imsite/imfreeware.htm