X-Lite

Jitsi (previously SIP Communicator) is an audio/video and chat communicator that supports protocols such as SIP, XMPP/Jabber, AIM/ICQ, Windows Live, Yahoo! and many other useful features. Jitsi is...

Ekiga (formely known as GnomeMeeting) is an open source VoIP and video conferencing application for GNOME. Ekiga uses both the H.323 and SIP protocols. It supports many audio and video …

Linphone is an internet phone or Voice Over IP phone (VoIP). With linphone you can communicate freely with people over the internet, with voice, video, and text instant messaging. Linphone …

QuteCom is a community of enthusiasts and developers, creating free software products related to communication over IP. The flagship product of the QuteCom project is a softphone which allows you …

Psi+ is a development branch of Psi IM XMPP/Jabber client. Psi is a cross-platform powerful XMPP/Jabber client (Qt, C++) designed for the Jabber power users.

SFLphone is a robust standards-compliant enterprise softphone, for desktop and embedded systems. It is designed to handle several hundreds of calls a day. SFLphone is available under the GNU GPL …

Blink, a state of the art, easy to use SIP client. You can use it with any SIP provider or its own fully-featured SIP service. Voice over IP * HD …

Zoiper IAX & SIP multilanguage and multiplatform (Windows, Linux and Mac OS X) softphone is a VoIP soft client, meant to work with any IP-based communications systems and infrastructure. Zoiper …

Allegedly "cheap" phone calls with Jumblo. WARNING: expect to have payments disappear with zero recourse and have "free" minutes widely unavailable like any other betamax clone scam.