Full-featured instant messaging software.

iChat AV is an AOL Instant Messenger (AIM), .Mac, ICQ and XMPP client by Apple Inc. for their Mac OS X operating system. Using a Jabber-like protocol and Bonjour for user discovery, it also allows for LAN communication. iChat's AIM support is fully endorsed by AOL, and uses their official implementation of the AIM OSCAR protocol. Using a Jabber transport, iChat users may also integrate their MSN and Yahoo! contacts into the Jabber pane.

MSN Messenger is a freeware instant messaging client that was developed and distributed by Microsoft in 1999 to 2005 and in 2007 for computers running the Microsoft Windows operating system (except Windows Vista), and aimed towards home users. It was renamed Windows Live Messenger in February 2006 as part of Microsoft's Windows Live series of online services and software.

Windows Messenger is a proprietary instant messaging client included in Microsoft's Windows XP operating system. It is also available for Windows 2000 and Windows Server 2003, beginning with version 5, but is not included in Windows Vista. Windows Messenger should not be confused with the similarly-named Windows Live Messenger (formerly known as MSN Messenger), which is a separate instant messaging product available for download from Microsoft. It is also not related to the Messenger Service, which is a component of Windows NT's LAN Manager.

Yahoo! Messenger is a popular advertisement-supported instant messaging client and associated protocol provided by Yahoo!. Yahoo! Messenger is provided free of charge and can be downloaded and used with a generic "Yahoo! ID" which also allows access to other Yahoo! services, such as Yahoo! Mail, where users can be automatically notified when they receive new email. Yahoo! also offers PC-PC, PC-Phone and Phone-to-PC service, file transfers, webcam hosting, text messaging service, and chat rooms in various categories.