Instant messaging

Skype

Free your conversations.
Skype-to-Skype calls are always free - but that’s just the start.
http://www.skype.com/go/download/

Windows Live Messenger

Connect and share instantly on the world’s most popular IM network
http://ideas.live.com/

ICQ

Welcome to ICQ, the largest multi lingual community on the Web! Download ICQ, meet new friends, find old pals and get together with people around the world!
http://www.icq.com/

Agile Messenger

Agile Messenger is the most feature rich and versatile Instant Messenger for mobile phones on the market today.
http://www.agilemobile.com/agile_messenger.html

Yahoo! Messenger (8.1)