VoIP card : IP PBX,VoIP phone system,Asterisk PBX,ISDN PRI card-- VoIP manufacturer

Free software and open-source license
Asterisk - an open source SIP/IAX PBX
The Open Source SIP PBX (also available in commercially supported form Pingtel)
Axon PBX - Free SIP PBX (Windows)
YATE - a professional open source SIP, H.323,IAX PBX and client. It works as a SIP-H.323 translator. (supported commercially by Null Team)

SIP communications products

Proprietary license
IntTalk Enterprise VoIP solutions softphone, SIP MCU and more.
CommuniGate Pro IP Communications Platform - Carrier Class Internet Communications Platform
Objectworld UC Server Unified Communications for Windows.
MessengerSDK SIP based voice and video telephony SDK.
3CX Phone System for Windows SIP server.
Brekeke PBX and Brekeke SIP Server
IVR Technologies, Inc. Talking SIP 3.0 an integrated application, media and real-time billing server
Vonexus Microsoft-based IP Telephony Solution.
Microsoft Office Live Communications Server
Creacode NicIVR Advanced SIP IVR and application development platform
Pactolus SIPware solutions carrier-grade calling card, broadband telephony, conferencing, and custom applications
Rostrvm Switchless standards based call centre architecture using SIP.
pbxnSIP SIP-based PBX for Windows
Dialexia Dial-Office SIP-based IP-PBX for both Windows and Linux.
3Com SIP PBX Enterprise IP Telephony applications suite using SIP.
Xeepe Hybrid SIP/ISDN Phone System for SOHO and SMB.

SIP servers

Free software and open-source license
YATE Yet Another Telephony Engine - An H.323, SIP, IAX server and client for both Windows and Linux made for Enterprise environment.
Mobicents - The Open Source JSLEE and SIP Server
SIProxd SIP proxy - a proxy/masquerading daemon for the SIP protocol
SIPX, for Linux.
Asterisk (PBX) SIP IAX/MGCP/H323 and more
OpenSER - GPL SIP Server focused on security and scalability
OpenSBC - Reference implementation of Session Border Controller (including simple proxy and registrar) using the MPL licensed
SIP Express Router (SER) - GPL SIP Server of iptel.org, focused on security and scalability
YXA is SIP software written in Erlang
CallWeaver - OpenSource telephony server

Proprietary license
Avaya Communication Manager SIP Enablement Services
BEA Systems WebLogic SIP Server
Brekeke SIP Server is available for Windows, Linux, Mac OS X and Solaris. It is free for personal and educational use.
Creacode NicSC SIP Session Border Controller] High performance SIP Call Controller, Registrar and NAT Traversal solution.
Eyeball SIP Proxy Server
IVR Technologies, Inc. Talking SIP 3.0 - An integrated application, media and real-time billing server
Nortel SIP Multimedia Communication Server 5200
Pactolus RapidFLEX Service Delivery Platform - Highly scalable SIP application server, media server, and service creation environment
Paradial RealSIP Server
Cisco SIP Proxy Server
Pingtel Call Manager (based on SIP Foundry open source)
Ubiquity SIP Application Server
3Com VCX IP Telephony Module: Back-to-Back User Agent SIP PBX
Oracle Multimedia communication Engine (M2CE)
Interactive Intelligence SIP Proxy, specialising in Load Balancing and Fault Tolerance
CommuniGate Pro - universal communication server - SIP Proxy/Registrar, NAT Traversal/SBC, IVR, Conference, IM/Presence via SIMPLE/XMPP, E-Mail and GroupWare.
Communology SIP Clients, specialising in mobile Clients and SIP testing
Squire Technologies SIP H323 SBC Class 4 softswitch

SIP-capable firewalls
Secure Computing's SnapGear firewall includes the SIProxd SIP proxy
Intertex SIP Transparent Routers, Firewalls and ADSL modems - For broadband deployments and the SOHO market
Ingate SIP Transparent Enterprise Firewalls and SIParators - Enabling global SIP communication on the enterprise LAN
Secure Computing's Sidewinder 7 firewall includes a SIP proxy
Balabit IT Security Zorp Professional firewall includes SIP proxy
BorderWare SIPassure firewall translates TLS and SRTP

SIP clients

Free software
Ekiga, formerly known as GnomeMeeting, GPL
KCall, using Qt libraries
KPhone, using Qt libraries, GPL
YATE - An H.323, SIP, IAX server and client for both Windows and GNU/Linux, license GPL with an embedded browser.
OpenWengo - A SIP based softphone and IM client using the Qt libraries, available under the GPL
PhoneGaim, based on Gaim.
PJSUA, light SIP stack in C (designed for embedded system) with command line interface, GPL
TudoMais, Java/Flash-based for Windows.
Zap!' is cross platform, based on XULRunner, licensed under the MPL
SIP Communicator, the Java VoIP and Instant Messaging client, runs on Windows, Linux and Mac OS X, LGPL
Linphone, with a core/UI separation, the GUI is using GTK+ libraries
MiniSIP, with a core/UI separation and encryption, alpha version for Nokia 770
Twinkle, using Qt libraries
XMeeting is Mac OS X SIP/H.323 client, based on OpenH323 libraries, licensed under the MPL
wxCommunicator, based on SIPXtapi and wxWidgets libraries, GPL

Proprietary freeware
Microsoft Windows Messenger (not to be confused with MSN Messenger or Windows Live Messenger)
SJphone runs on Windows, Mac OS X, Linux and PocketPC.
Tivi runs on Windows
NCH Swift Sound Express Talk, GSM, uLaw, ALaw and PCM codecs
3CX Phone for Windows - a free SIP client for Windows.
Mindspring, for Windows. Voice, chatting, and file-sharing capabilities.
RadiusCat for Windows, SIP RADIUS AAA Billing Software
CounterPath X-Lite for Windows, Mac OS X and Linux
The Cornfed SIP User Agent for Linux by Cornfed Systems is available with Command-Line Interface (CLI) and Gnome GUI clients.
Gizmo Project for Windows, Mac OS X and Linux, primarily used for the SIPphone network
SightSpeed for Windows and Mac OS X. G.711, iLBC, Speex and H.263 codecs
Phoner for Windows, G.711, iLBC, G.726, GSM and Speex codecs
PhonerLite for Windows, G.711, iLBC, G.726, GSM and Speex codecs
fring enables users to make mVoIP (mobile VoIP) calls with any SIP provider even from non-SIP enabled phones

Commercial proprietary software
AGEphone runs on Windows, PocketPC and Windows Mobile.
Hampton Software's Articulation runs on Palm OS 5 handhelds including Clie and Treo.
is-phone integrated softphone, Session Initiation Protocol (SIP) based, PBX independent
Movial PC, Symbian and Windows CE Clients
Pingtel, Java-based for Windows.
VeriCall Edge for voice/video over IP calling runs on embedded Linux.
Virbiage Cubix for Windows, Inter-Asterisk eXchange Protocol, G.711, iLBC, G.729, GSM and Speex codecs
CounterPath X-Pro for Windows
SightSpeed for Windows and Apple OSX G.711, iLBC, ADPCM and Speex codecs

SIP test tools

Proprietary license
SFTF: SIP Forum User Agent Test Framework (open source; written by the SIP Forum).
Codenomicon SIP Test Tool: Commercial SIP robustness and security test tool (next generation PROTOS SIP test tool [see open source test tools])
Mu Security: Commercial SIP-VoIP, RTSP-IPTV Triple Play security analysis & testing platform (automate existing 3rd party testing and scripts like Nessus and PROTOS
Bandwidth.com offer a tool to test the SIP ports on your network
SIPient Systems - SIPFlow: SIPFlow captures SIP traffic and draws callflows (ladder diagrams) for each transaction.

Free software and open-source license
SIPp - an Open Source SIP test tool (functional and performance tests).
SIPsak - a command line tool which can send simple requests to a SIP server (Open Source).
PROTOS c07-SIP test suite: PROTOS c07-SIP robustness and security test suite (initial results of running the test suite are documented in US/CERT advisory).
pjSIP-perf - an Open Source SIP transaction/call performance measurement tool.
Asteroid - is a SIP Denial of Service testing tool. See MITRE CVE-2006-5444 and CVE-2006-5445

SIP protocol stacks

HelloSoft Ltd. Voip protocol for wlan, cellular & gateway, including SIP Stack, Voice Media Processing, Jitter Buffering, Call Control Manager.
VeriCall Edge integrates its own SIP stack with all of the required media processing, packet handling and call control functionality needed to develop voice/video over IP end-user devices.
amSIP SIP/audio/video SDK based on oSIP/eXoSIP2/oRTP/mediastreamer2 for softphone/server developments.
Proprietary license
RADVISION SIP Developer Suite for developing carrier-grade IMS Compliant SIP Client and Server applications on any platform.
The Cornfed SIP User Agent System Developer's Kit (SDK) for Linux by Cornfed Systems is available for integrating fully integrated softphones into OEM product designs.
Ulticom Signalware? SIP is a carrier-grade SIP stack designed for operator core networks
SIP .NET: SIP client API for .NET Framework and .NET Compact Framework
Ageet Corporation offers the small and fast microSIP stack

Free software and open-source license

Open SIP Stack - Free Software Open source C++ SIP stack released under MPL 1.0 license. Designed for scalability and reliability.
GNU oSIP - Free Software Open source (also available under commercial license) C SIP stack released under the LGPL. Small footprint. Support Linux/Win32/MacOSX/WM5.0/VxWorks. Designed for a basic library in order to develop SIP client & gateway.
eXoSIP - Free Software Open source (also available under commercial license) C SIP stack based on oSIP and released under the GPL. Support Linux/Win32/MacOSX/WM5.0/VxWorks. Designed for a basic library in order to develop SIP client.
ReSIProcate: Free Software SIP stack
Sofia-SIP - a Free Software SIP user agent library licensed under the LGPL. It can be utilized conditionally in the IMS network.
JAIN-SIP JAVA SIP Stack - Public domain implementation of RFC 3261 and extensions. Reference Implementation for JSR 32 javax.SIP package.
PJSIP: Open Source SIP stack in C. Tiny footprint, ultra portable, and very fast.
Yass - Yet Another SIP stack and is the YATE SIP stack written in C++. It can be used under Windows or Linux in a single or multithread environment for state-full software like clients, servers and proxies. It contains a transaction engine and of course a SIP not very efficient but safe parser.