Partysip is an implementation of a SIP proxy server. SIP stands for the Session Initiation Protocol and is described by the rfc2543 (soon to be deprecated by latest revisions). SIP is a open standard replacement from IETF for H323. Partysip is a modular application where some capabilities are added and removed through plugins. The program comes with several GPL plugins. At this step, partysip and its plugins could be used as a 'SIP registrar', a 'SIP redirect server' and a 'SIP statefull proxy server'. (stateless capabilities have been removed) WWW: http://www.partysip.org/