Google Talk (GTalk) is a free Windows and web-based application for instant messaging and voice over internet protocol (VOIP), offered by Google Inc. The first beta version of the program was released on August 24, 2005.
Instant messaging between the Google Talk servers and its clients uses an open protocol, XMPP, allowing users of other XMPP clients to communicate with Google Talk users. V0IP in Google Talk is based around the Jingle protocol. The technology used within the Google server network however is not publicly known. through google talk you send instant message through messanger. other competitor are yahoo messanger and rediff bol which provide same service.
The Google Talk client is only available for Microsoft Windows (2000, XP, Server 2003, Vista and Windows 7). Mobile clients are also available for the BlackBerry, iPhone and T-Mobile G1 On February 7, 2006, Gmail received chat functionality using Ajax for server–browser communication, and was integrated with Google Talk.
Users can send instant messages to other Gmail users. As it works within a browser, Google Talk does not need to be downloaded to send instant messages to Gmail users. The connection between the Google Talk client and the Google Talk server is encrypted, except when using Gmail's chat over HTTP. On July 28, 2006, Google added voicemail and file sending capabilities to the Google Talk client. Voicemail messages can be 10 minutes long.