An open standard for instant messaging (IM). There are tens of thousands of Jabber servers on the Internet, most of which are privately run within a company or college campus. There are also hundreds of public Jabber servers that any user can register with, Google Talk being the largest at one time.
The Jabber protocol is XMPP (Extensible Messaging and Presence Protocol), and any client program that supports XMPP can communicate with any other user with an XMPP client, providing the sender is in the recipient's contact list (buddy list). Multi-protocol IM clients support XMPP along with proprietary IM services such as AOL/AIM, ICQ, MSN and Yahoo!; however, an IM account must be opened with each service.
There are numerous open source implementations of Jabber clients and servers, including the original Jabber at www.jabber.org.
Jabber is like email with users communicating from domain to domain. For example, a Jabber server at computerlanguage.com can connect with the Jabber server at gmail.com (Google's IM domain). Jabber also supports access to non-XMPP systems by connecting a "transport" to the Jabber server that provides a gateway to that IM protocol. However, if a public Jabber server with thousands of users employs a gateway, chances are the proprietary IM service will eventually block its IP address, since a huge amount of traffic coming from one IP address is generally not tolerated.
There were commercial implementations of Jabber, the most notable of which was from Jabber, Inc. founded in 2000, soon after Jabber was developed. In 2008, the company was acquired by Cisco, which also offers Jabber desktop videoconferencing. See instant messaging