minisip

minisip is a SIP VoIP soft phone that implements additional security features such as mutual authentication, encryption and integrity of on-going calls, and encryption of the signaling (SIP over TLS). These security features use work-in-progress IETF standards (SRTP and MIKEY).
OhPhone

OhPhone is a H.323 Video Conferencing Program compatible with other H.323 video conferencing programs including Microsoft NetMeeting.

OhPhone supports full duplex audio and bi-directional video. It requires a full duplex sound card for audio support and a Bt848/878 based video card (using the bktr driver) for video capture.

OhPhone uses the OpenH323 and PWLib libraries, developed by Equivalence Pty.
Microsoft NetMeeting

NetMeeting is Microsoft's free H.323-compliant VoIP software phone for Windows.
Internet Switchboard

The Internet SwitchBoard software is the client software for MicroTelco services and is included with the purchase of the Internet PhoneJACK or Internet PhoneCARD.

The Internet Switchboard was designed to be used with Quicknet hardware and a MicroTelco Services account. The Internet SwitchBoard can be configured with your firewall and features voice control with worldwide phone and dial tone emulation.

The Internet SwitchBoard software is a PC-to-PC, PC-to-Phone, Fax-to-Email, and Fax-to-Fax calling application that allows users to make low cost calls worldwide to other phones or fax machines.

PC-to-Phone and Fax-to-Fax calls are as easy to dial as using a phone or fax machine. PC-to-PC calls are made by dialing an IP address and are free. FAX-to-Email documents are electronically transmitted as virus free e-mail attachments and are free if sent individually. Recipients can view files in popular e-mail clients.

Internet Switchboard features include:

* Low calling rates through MicroTelco Services
* Auto call connect - automatic connection and least cost routing feature that connects your call using the next available carrier when the chosen carrier is unavailable
* Least cost routing - for voice amongst leading global IP carriers
* Automatic firewall detection
* Automatic fax detection - allowing a fax machine to be plugged into a compatible card using the Internet SwitchBoard and route faxes to email or another fax machine via the Internet
* International phone emulation's & connectivity
* Low account balance warning
* Call connect announcement
* Auto gain control
* Supports any type of Internet connection, including broadband
* Microsoft Operating support including Windows 98/98SE, ME, 2000, and Windows XP

SIPSet

SIPSet is a SIP User Agent with a GUI front end that works with the Vovida SIP stack. You can use the SIPSet as a soft phone, to make and receives phone calls from your Linux PC.

The current release of SIPSet implements these features and functionality:

* SIPSet can make calls through a SIP proxy.
* SIPSet can register to receive calls through a SIP proxy.
* SIPSet can make and receive calls directly with another User Agent.

KPhone

KPhone is a SIP User Agent for Linux. It implements the functionality of a VoIP Softphone but is not restricted to this. KPhone is licensed under the GNU General Public License. KPhone is written in C++ and uses Qt.
Jabbin

Jabbin is an open source Jabber client program that allows free PC to PC calls using VoIP over the Jabber network.
Free VoIP Gateways
isdnh323

isdn2h323 is a Linux based H.323 - ISDN gateway. At the moment the gateway supports the following features:

* ISDN and H.323 users can initiate a connection.
* The number of simultaneous incoming and outgoing calls is limited by the number of available ISDN channels only.
* H.323 users can specify the ISDN number of the other party.
* The gateway's administrator can assign an ISDN MSN to a H.323 user. This makes it possible for an ISDN user to call a H.323 user directly. The gateway will choose the H.323 user id depending on the called ISDN MSN.
* The gateway discovers an available H.323 gatekeeper and registers with the gatekeeper. It's possible to specify one or more phone prefixes the gateway is responsible for.
* ISDN's touch-tones (DTMF) are translated to H.323's user input messages and vice versa.
* Automatic gain control (AGC)
* Automatic echo compensation (AEC)
* To avoid security problems the gateway offers an option to restrict the IPs allowed to use the gateway for an outgoing ISDN call.
* The status of the lines and the configuration of the gateway are written to a HTML file.
* Errors and other information are logged using Linux's syslog() feature.
* Three H.323 codecs are supported: ALaw, muLaw, and GSM.
* Least Cost Router

PSTNGw

PSTNGw is a very simple PSTN to H.323 gateway program using the OpenH323 library. It allows H.323 clients to make outgoing calls, and incoming calls to be routed to a specific H.323 client.

PSTNGw makes use of PWLib and the OpenH323 stack from Equivalence Ltd Pty.
SIPRG (SIP Residential Gateway)

The SIP Residential Gateway (SIPRG) is an open source application based on the Session Initiation Protocol (SIP). The SIPRG is an IP Telephony Gateway that allows a SIP User Agent to make and receive calls between the Public Switched Telephone Network (PSTN) and a SIP-based network such as VOCAL.

The SIPRG was developed with the VOVIDA SIP stack version 1.3.0, and uses a QuickNet LineJACK card for connecting an Analog telephone line. Currently, it supports only a single LineJACK card and is therefore a single-line gateway.
Free VoIP Gatekeepers
OpenH323 Gatekeeper - The GNU Gatekeeper

The OpenH323 Gatekeeper is a full featured H.323 gatekeeper, available freely under GPL license. It is based on the Open H.323 stack. Both components together form the basis for a free IP telephony system (VOIP).

OpenH323 Gatekeeper currently supports Linux, Microsoft Windows, FreeBSD, Solaris and MacOS X.
Opengatekeeper

OpenGatekeeper is an Open Source H.323 Gatekeeper based on the work done by the OpenH323 project.

OpenGatekeeper runs on Linux, FreeBSD and Win32 platforms.

OpenGatekeeper supports all the basic features of an H.323 Gatekeeper such as registration, admissions and access control, address translation and bandwidth monitoring and control.

OpenGateKeeper also supports many advanced features such as:

* Gatekeeper routed calls
* Support of H.323v2 alias types (party number, URL, transport id and email address)
* Support for gateway prefixes
* Registration and call activity logs
* Neighbour gatekeeper database
* Registration time to live