Chatting & Messaging

X-Chat
XChat is an IRC chat program for both Linux and Windows. It allows you to join multiple IRC channels (chat rooms) at the same time, talk publicly, private one-on-one conversations etc. Even file transfers are possible.

mIRC
mIRC is a popular Internet Relay Chat client used by millions of people, and thousands of organizations, to communicate, share, play and work with each other on IRC networks around the world. Serving the Internet community  for over a decade, mIRC has evolved into a powerful, reliable and fun piece of technology.

Windows Live (MSN) Messenger
Instantly connect to the people who matter the most—via text, voice, or video. Even if they’re offline, you can leave a message or send a note.

Miranda IM
Miranda IM is a multi-protocol instant messaging client for Windows. Very light on system resources and extremely fast, Miranda IM requires no installation and can be made to fit on a single floppy disk or USB drive. Featuring a powerful plugin-based framework and boasting over 350 plugins, Miranda IM is one of the most flexible and customisable messaging clients on the planet.

Pidgin
Pidgin (formerly named Gaim) is a multi-platform instant messaging client. The software supports many commonly used instant messaging protocols, allowing the user to log into various different services from one application.

Trillian
Trillian is a proprietary multiprotocol instant messaging application for Windows created by Cerulean Studios that can connect to multiple IM services, such as AIM, ICQ, Windows Live Messenger, Yahoo! Messenger, IRC, Novell GroupWise Messenger, Bonjour, Jabber, and Skype networks (the latter four with Trillian Pro which allows for additional plugins).