Instant messaging (IM) is a form of real-time direct text-based communication between two or more people using personal computers or other devices, along with shared software clients. The user’s text is conveyed over a network, such as the Internet. More advanced instant messaging software clients also allow enhanced modes of communication, such as live voice or video calling.
Web Based :
Gmail has instant messaging capacity in webpage itself, which can be used in a web browser without need of IM client download and install. Later Yahoo and Hotmail also implemented it. Meebo website offers instant messaging of different IM services. Generally such services are limited to text chat, voice and video are not available.
Meebo is an instant messaging program which supports multiple IM services, including Yahoo! Messenger, Windows Live Messenger, AIM, ICQ, MySpaceIM, Facebook Chat, Jabber, Google Talk, Myyearbook IM and XMPP; it is based on the free and open source library libpurple created by the software developers of Pidgin.
imo.im is a web-based service that allows users to hold text, voice, and video chats on multiple instant messaging protocols. Currently supported protocols include AIM, Google Talk, ICQ, MSN, MySpace, Skype, and Yahoo Messenger. The service is free and requires no user-registration or sign-up.
eBuddy Web Messenger is a web based instant messaging service. Chat online with friends on MSN, Yahoo, AIM, ICQ, GTalk, Facebook and MySpace IM
fring™ is a mobile internet service & community that enables users to talk, chat & interact with other fringsters™ and their online communities, from their mobile phones.
Nimbuzz is a multi community mobile social messenging and VoIP provider, combining VoIP, instant messaging, and (geo) presence. The free application lets users connect and interact with their buddies across popular communities, including Skype, Windows Live Messenger, Yahoo! Messenger, ICQ, Google Talk (Orkut), AIM, and social networks including Facebook and MySpace.
3.ebuddy for mobile
All your MSN, Yahoo!, AIM, ICQ, Google Talk and Facebook buddies in one single buddylist!