Google Talk is an instant message and VoIP service provided by Google.
The Google Talk software is available for Windows XP and later editions, Linux and Mac. Versions are available in the main western European languages, Turkish, Russian, Chinese and Japanese amongst others. You need Gmail, Google+, iGoogle, orkut or Chrome OS to subscribe.
Google Talk is based on the Jabber/XMPP protocol and is compatible with other instant message software such as Adium, GAIM, Trilian Pro and above all iChat, the instant message software supplied with Mac OS X by Apple.
For voice communication, Google talk supports the PCMA, PCMU, G.723, iLBC codecs and the Global IP Sound codecs: ISAC, IPCMWB, EG711U, EG711A and is envisaging adoption of the "SIP" telecom standard.