XMPP

Extensible Messaging and Presence Protocol (XMPP) is a communications protocol for message-oriented middleware based on XML (Extensible Markup Language). The protocol was originally named Jabber, and was developed by the Jabber open-source community in 1999 for near real-time, instant messaging (IM), presence information, and contact list maintenance. Designed to be extensible, the protocol has also been used for publish-subscribe systems, signalling for VoIP, video, file transfer, gaming, Internet of Things applications such as the smart grid, and social networking services.

Protocols
Anonymity
I2P
Tor
Communication
DNS
IRC
Matrix
SIP
Tox
XMPP
Encryption
GPG
OMEMO
OTR
S/MIME
SSL/TLS
ZRTP
Synchronization
ActiveSync
CalDAV
CardDAV
WebDAV
Syndication
RSS