Google Talk is a freeware

Freeware

Freeware is computer software that is available for use at no cost or for an optional fee, but usually with one or more restricted usage rights. Freeware is in contrast to commercial software, which is typically sold for profit, but might be distributed for a business or commercial purpose in the...

 voice over Internet protocol

Voice over IP

Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...

 (VoIP) client application offered by Google Inc. The first beta version of the program was released on August 24, 2005. It is available for the Android operating system, GNU/Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

, Intel Mac OS X 10.5

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 or later, Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 (XP

Windows XP

Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...

, Server 2003

Windows Server 2003

Windows Server 2003 is a server operating system produced by Microsoft, introduced on 24 April 2003. An updated version, Windows Server 2003 R2, was released to manufacturing on 6 December 2005...

, Vista

Windows Vista

Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...

, and Windows 7), and Google Chrome OS

Google Chrome OS

Google Chrome OS is a Linux-based operating system designed by Google to work exclusively with web applications. Google announced the operating system on July 7, 2009 and made it an open source project, called Chromium OS, that November....

.

Instant messaging between the Google Talk servers and its clients uses an open protocol, XMPP

Extensible Messaging and Presence Protocol

Extensible Messaging and Presence Protocol is an open-standard communications protocol for message-oriented middleware based on XML . The protocol was originally named Jabber, and was developed by the Jabber open-source community in 1999 for near-real-time, extensible instant messaging , presence...

, allowing users of other XMPP/Jabber clients to communicate with Google Talk users.