Asterisk - The Open Source Linux PBX and Telephony Platform
- A complete Linux PBX (private branch exchange) software for VoIP networks; it is inter-operable with almost all standards-based telephony equipment using relatively inexpensive hardware.
Asterisk Documentation Project - Asterisk: The Future of Telephony--Online Book
- This detailed guide to Asterisk covers installation, configuration, and integration of Asterisk with existing phone systems, without the need for additional hardware. Available for download in PDF format. Published by O'Reilly, 2nd edition, 2007.
Building an Asterisk@Home Test Lab
- Links to a three-part series on setting up a small production Asterisk iPBX on the cheap. Aimed at Linux and telephony noobs. (2006) Information in these three articles is still relevant today. (2008)
Ekiga - Free Your Speech
- A GPLed SIP and H.323-compatible VoIP, IP telephony, and video conferencing application; formerly called GnomeMeeting. Latest stable release is 3.2.4, 2009-05-20.
Free Telephony Project
- The goal of this project is to provide free hardware designs for telephone systems. Both the hardware and software are free and open.
GNU Bayonne - Telephony Server of the GNU Project
- GNU Bayonne offers free, scalable, media independent software environment for development and deployment of telephony solutions for use with current and next generation telephone networks. Latest release of Bayonne 2 is 2.3.3, 2008-08-13.
GNU Gatekeeper - OpenH323 Gatekeeper
- A full-featured H.323 gatekeeper, available freely under GPL license. It forms the basis for a free IP telephony system (VOIP). Multilingual documentation available. Latest release is 2.2.7, 2008-04-02.
KPhone
- An Internet phone application for Linux. Latest version is 1.2, 2008-11-22.
Kiax - an IAX Softphone
- A software phone (soft phone, VoIP client) with a simple and comfortable user interface for making VoIP calls to Asterisk PBX. Internationalization is excellent -- available in 10+ languages. Latest release (beta) is 2.1, 2009-01-13.
Linphone
- An internet phone or Voice Over IP phone (VoIP). Latest stable release is 3.0.0, 2008-10-12. Site also available French.
LinuxMCE
- An open source software platform designed to allow a computer to act as a home theater PC (HTPC), personal video recorder, full-featured VOIP-compatible phone system, and a home automation system.
Network Caller ID (NCID)
- A cross-platform client/server network caller ID package, which features include support for multiple clients and caller ID systems, name and number aliasing, call logging, and a TiVo client. Latest stable release is 0.72, 2008-12-24.
QuteCom
- A GPL-licensed, cross-platform telephony software. Previously known as WengoPhone.
Speak-Freely
- A cross-platform Internet telephony (Voice Chat) application; latest version: 7.6a, 2004.
Tribox
- An Asterisk-based BPX phone system for small-to-medium size businesses. Current stable release is 2.6.2, 2008-12-26. Formerly called Asterisk@Home.
Twinkle
- A telephony application for voice over IP communcations using the Session Initiation Protocol (SIP). Latest stable release is 1.4.2, 2009-02-25.
VoIP Wiki
- A reference/resource guide for VoIP (Voice over IP) networks including software, hardware, service providers, reviews, configurations, standards, tips & tricks and everything else related to VoIP networks, IP and Internet telephony.
VoIP-4D Primer - Online Book
- This guide, geared to both technical and non-technical readers, deals with building voice infrastructure. The examples in this guide provide essential background for building low-cost telephony systems. Available for download [1.8 MB] in Arabic, English, French, and Spanish. (2006)
Yate - Yet Another Telephony Engine
- An extensible telephony engine for VoIP and PSTN (Public Switched Telephone Network); voice, video, data and instant messaging can all be unified under this flexible routing engine. Latest release is 2.0.0, 2008-08-04.