Dorgem
Dorgem is a webcam capture application for Windows 9x and up.
Ekiga
Ekiga (formerly known as GnomeMeeting) is an open source VoIP and video conferencing application.
OpenH323
The OpenH323 project provides full featured, interoperable, Open Source implementation of the ITU H.323 teleconferencing protocol that can be used by personal developers and commercial users without charge.
Speak-Freely
Speak Freely is a Cross Platform Internet telephony (Voice Chat) application which provides high quality voice grade audio with GSM and CELP compression and encryption with DES, Blowfish, and IDEA ciphers.
Asterisk
Asterisk is a complete PBX in software.
SIP Communicator
SIP Communicator is an audio/video Internet phone and instant messenger written in Java.
sipXecs IP PBX
sipXecs IP PBX is the leading open source IP PBX.
SIPp
SIPp is a free Open Source test tool / traffic generator for the SIP protocol.
QuteCom
QuteCom (previously called WengoPhone) is a SIP compliant VoIP client developed by the QuteCom (previously OpenWengo) community.
Phone Gaim
PhoneGaim is the All-In-One Instant Messaging and Internet Calling solution for your personal computer Introducing PhoneGaim, the easiest way to make phone calls to anybody in the world with just a few clicks using an easy interface that you are already familiar with.
OpalVoip
Open Phone Abstraction Library (OPAL) is a C++ multi-platform, multi-protocol library for Fax, Video & Voice over IP and other networks.