Web Directory

» Asterisk
   Open Source telephony switching and private branch exchange (PBX) daemon. Supported signalling protocols: H.323, SIP, MGCP, SCCP (Cisco Skinny).
   http://asterisk.org

» Ekiga
   Videoconferencing application to make audio and video calls to remote users. Supports both SIP and H.323.
   http://www.ekiga.org/

» GNU Bayonne
   A free, scalable telecommunications application server by the GNU Project.
   http://www.gnu.org/software/bayonne/bayonne.html

» GNU oSIP
   Implementation of Session Initiation Protocol (SIP). This library provides an interface to initiate and control SIP based sessions.
   http://www.gnu.org/software/osip/osip.html

» KPhone
   SIP based VoIP user agent. It supports Presence and Instant Messaging.
   http://sourceforge.net/projects/kphone

» Linphone
   SIP based web phone. Supported audio codecs are G711, LPC10-15, GSM, and SPEEX.
   http://www.linphone.org/

» Minisip
   SIP based phone. Supports video, communication encryption and push-to-talk.
   http://www.minisip.org/

» NAT H323 under Linux
   Mini-HOWTO for NAT and H.323 - configuring Linux to support H.323 while using network address translation.
   http://pierre.clerissi.free.fr/uHOWTO/nath323.html

» Nautilus Secure Phone
   Program that allows two parties to hold a secure voice conversation using Linux and TCP/IP.
   http://nautilus.berlios.de/

» OpenH323 Gatekeeper
   Free H.323 gatekeeper (GPL) based on OpenH323.
   http://www.gnugk.org/

» Partysip
   SIP proxy server. It can operate as registrar server, redirect server and stateful proxy server. SIP is an open standard (IETF) replacement for H323.
   http://www.nongnu.org/partysip/partysip.html

» Siproxd Project
   Proxy/masquerading daemon for the SIP protocol. It handles registrations of SIP clients on a private IP network and performs rewriting of the SIP message bodies to make SIP connections work via a masquerading firewall (NAT).
   http://siproxd.sourceforge.net/

» Skype
   Peer to peer voice service. Users may call landlines and cellphones for a fee; users may call each other for free. Source code is not available.
   http://www.skype.com/