About Apache Vysper 

This project aims at delivering a server implementation of both the core and IM parts of the XMPP protocol 
(as specified in RFCs 3920 [1] + 3921 [2]).

"Vysper" is pronounced like in "whisper".

XMPP[3] is an open, secure and extensible instant messaging protocol which has evolved from Jabber.
It provides interoperability features for communication with other XMPP and non-XMPP servers.
It is used and supported by many IM applications, both client and server.

The protocol and its many extensions (called XEPs) are maintained by the XMPP Standards Foundation (XSF) [4].

[1] http://www.ietf.org/rfc/rfc3920.txt
[2] http://www.ietf.org/rfc/rfc3921.txt
[3] http://en.wikipedia.org/wiki/XMPP
[4] http://www.xmpp.org/