Asterisk - The Open Source Linux PBX
- 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)
Ekiga - Free Your Speech
- A GPLed SIP and H.323-compatible VoIP, IP telephony, and video conferencing application; formerly called GnomeMeeting.
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 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 1.0.2.1, 2006-09-22.
Kiax - Just Talk!
- A software phone (soft phone, VoIP client) with a simple and comfortable user interface for making VoIP calls to Asterisk PBX.
LiPS (Linux Phone Standards) Forum
- A consortium of telephony operators, device manufacturers, silicon and software vendors formed for the purpose of defining standards for Linux-based telephony applications
Linphone
- An internet phone or Voice Over IP phone (VoIP). Latest release is 2.0.0, 2007-11-19.
Network Caller ID (NCID)
- A cross-platform client/server network caller ID package; features include support for multiple clients and caller ID systems, name and number aliasing, call logging, and a TiVo client.
Tribox
- An Asterisk-based BPX phone system for small-to-medium size businesses. Formerly called Asterisk@Home.
Twinkle
- A telephony application for voice over IP communcations using the Session Initiation Protocol (SIP).
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.