XMPPJabber

XMPP, short for Extensible Messaging and Presence Protocol, originated from the open-source Jabber project. It is a communications protocol designed for near-real-time exchange of structured data and is widely used for instant messaging, presence information, and contact management in a decentralized network.

Architecture and operation: XMPP uses XML streams to connect clients to servers and servers to other servers. Clients are addressed with a JID (Jabber ID) in the form user@domain/resource. Messages, presence updates, and roster (contact list) management are exchanged through servers using client-to-server and server-to-server connections. The network is federated, allowing users on separate domains to communicate.

Standards and extensions: The core protocol is standardized by the IETF as RFC 6120 (XMPP Core) and RFC 6121 (Presence and Roster). Many enhancements are defined as XMPP Extension Protocols (XEPs). Common extensions include multi-user chat (MUC), publish-subscribe (pubsub), message receipts, and message archiving.

Adoption and ecosystem: There are numerous XMPP servers (such as ejabberd, Prosody, Tigase) and clients (Pidgin, Conversations, Adium). Its decentralized nature enables interoperability across domains, making XMPP suitable for personal use, enterprise deployments, and integration into other services that require open, standards-based messaging and presence features.

Security: Security is primarily provided through TLS for server connections and SASL for authentication. End-to-end encryption can be achieved with third-party extensions like OMEMO or OTR, but is not guaranteed by the core protocol itself and depends on client and server configurations.