Jabber Software Foundation: http://www.jabber.org
Jabber Incorporated: http://www.jabber.com
An open XML protocol for the real-time exchange of messages and presence between any two points on the Internet. It provides a platform to implement many communication services. It can also be used for MachineToMachine communication. XML is used in the protocol so writing clients for it is very easy.
Jabber is client/server oriented but there is no central server. Instead, a network of servers are used. Jabber allows jabber clients to connect to other IM systems (ICQ, AIM, MSN Messenger) depending on the server. IRC support is claimed but is largely unmaintained.
- Jabber GaduGadu - Gateway
Even though Jabber is one of the few services that allows client-server confidentiality on most of its clients using the same technology almost all web browsers support, SSL, all the messages will be visible to the servers involved, and it will be possible to impersonate an user relying solely on this.
Some Jabber clients, however, do support PGP for encryption, but the fact that it doesn't sign outgoing messages is a serious security flaw if the server is out of the client's control or has been compromised. See Encrypted Chat Clients.