IPBX
- Asterisk PBX: http://asterisk.org
SIP
- SIP Express Router: http://www.iptel.org/ser
H.323
- OpenH323 Gatekeeper: http://www.openh323.org
- GNU Gatekeeper: http://www.gnugk.org
- OpenH323 Proxy: http://openh323.sourceforge.net
- H323 - ISDN Gateway: http://www.telos.de/linux/H323/
Conferencing/VoIP Software
- OpenMCU: http://www.openh323.org
Similar Clients
- XTen: http://www.xten.com
- XTen: http://www.xten.com
- SJPhone: http://www.sjlabs.com/
- OpenPhone: http://www.openh323.org
- Netmeeting: http://www.microsoft.com