Open source software has leading role in emerging of present Information and communication technologies (ICT), Following is list of top rated , mature and reliable open source applications that revolutionized the communication concepts.
IP Telephony applications
FreeSWITCH
A Cross-platform, Scalable, Stable Multi-Protocol Soft Switch ,The project inspired from renown Open Source asterisk PBX system but very well designed and has a bright future
http://www.freeswitch.orgAsterisk
A software-based, Open Source Converged PBX system that has revolutionized the traditional PBX industry
http://www.asterisk.orgKamailio
SIP proxy server, call router, and user agent registration server used in Voice over Internet Protocol and instant messaging applications.
http://www.kamailio.org/w/OpenSIPS
SIP proxy server, call router, registration server and redirect server suitable for internet telephony service providers to offer SIP based telephony services to their customers.
http://www.opensips.orgSipexes
SipX ECS (Enterprise Communications Server) is SIP based voice over IP telephony server, an ideal enterprise grade, SIP based communications system (IP PBX)
http://www.sipfoundry.orgGnugk
H.323 gatekeeper based on the OpenH323 stack. A gatekeeper provides address translation, admissions control, call routing, authorization and accounting services
http://www.gnugk.orgOpenSBC
Session Border Controller and B2BUA featuring Registrations, B2BUA, NAT traversal and ENUM
http://www.opensipstack.org
Asterisk & Freeswitch GUI interfaces
BlueBox
Latest monitoring and management tool, full-featured PBX GUI of freeswitch
http://www.2600hz.orgFreePBX
A full-featured PBX GUI supporting both asterisk and freeswitch
http://freepbx.orgElastix
An open source Unified Communications Server software that brings together IP PBX, email, IM, faxing and collaboration functionality
http://www.elastix.orgTrixBox
Web based asterisk PBX managment software utilizing best open source tools built over asterisk
http://www.trixbox.orgPBXinaflash
PBXinaflash is a web based asterisk PBX managment software built over asterisk like Elastix and Trixbox
http://pbxinaflash.net/Druid
Druid is unified communications platform for enterprises. It allows companies to deploy high end IP communications services using off the shelf hardware and IP phones.
http://www.voiceroute.orgVicidial
Vicidial ( Astguiclient ) is a professional web based inbound / outbound call center solution built over asterisk
http://astguiclient.sourceforge.net
Communications Frameworks
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Plivo is freeswitch based communication framework which provides web developers with basic building blocks to create voice based applications in the form of RESTXML and RESTAPI (REST-based APIs) also Plivo is compatible and works with Java, .NET, node.js, Perl, PHP, Python or Ruby programming languages.
http://www.plivo.org
Plivo
Communication Libraries
PJSIP
Pjsip is sip based open source high performance communication library with multimedia capabilities written in C language for building embedded/non-embedded VoIP applications.
http://www.pjsip.org/
Broadcasting Platform
ICTDialer
ICTDialler is next generation powerful auto dialler software that support sms messaging, fax broadcasting , voice broadcasting . It is bundled with IVR builder to create custom IVR with ease through web based drag and drop IVR Designer's tools .
http://www.ictdialer.org
Billing Systems
A2billing
A2Billing combined with Asterisk is a physical Telecom Platform and Soft-Switch providing a wide range of telecoms services using both traditional telephone technology or VoIP. It contains a real time billing engine
http://www.asterisk2billing.orgASTPP
A calling card voip solution built over asterisk and freeswitch
http://www.astpp.orgFreeside
Freeside is the premier open-source billing, CRM, trouble ticketing and provisioning automation software for wired and wireless ISPs, VoIP, hosting, service and content providers and other online businesses.
http://www.sisd.com/freesideCDRTool
a rating and mediation engine for Call Detail Records generated by opensips and others
http://www.ag-projects.com/CDRTool.htmlICTFAX
An email to fax gateway, supports G.711 faxing , PSTN faxing and T.38 origination and termination .ICTFAX is complete faxing solution
http://www.ictfax.orgCitrusDB
A Multi-user Billing solution for internet service, subscriptions, consulting, and telecommunications , It Provides CRM, Ticketing, Invoicing, and Credit Card Batches
http://www.citrusdb.org/
Voip softphones / Clients
Twinkle
Twinkle is sip based softphone and support both voice over IP and and instant messaging communications , It is sip standard compliant with advance features including secure voice communications using ZRTP / SRTP.
http://www.twinklephone.com//QuteCom
QuteCom is cross platform open source softphone supporting Voice, Video and IM with advance features also support SRTP, QuteCom is developed using Python , C and C++ .
http://trac.qutecom.org/wikiSFLphone
SFLphone is SIP and IAX based standards-compliant enterprise softphone, for desktop and embedded systems. It support Multi line and TLS / SRTP encryption
http://sflphone.org/
Mobile Clients
Csipsimple
A native android client based open source PJSIP library stack , secure version of Csipsimple also support ZRTP, SIP TLS and SRTP
http://code.google.com/p/csipsimple/Sipdroid
Sipdroid is native android client developed over PJSIP stack .
http://sipdroid.org/Siphon
Siphone is sip compliant Iphone client based on PJSIP SIP stack
http://code.google.com/p/siphon/
SIP Protocol Stacks and Libraries
eXosip
eXosip is a library that hides the complexity of using the SIP protocol for mutlimedia session establishement. This protocol is mainly to be used by VoIP telephony applications
http://savannah.nongnu.org/projects/exosip/Juphoon SIP Stack
Rich software SDK support SIP, SDP, XML, RTP/RTCP, HTTP, STUN, ABNF etc. Support Windows, Linux, ThreadX, Vxworks etc.
libdissipate SIP stack
http://www.juphoon.com/en/products/sip.htmLibre
Portable SIP Stack under BSD license with IPv4/v6 support (SIP,SDP,RTP/RTCP,STUN,TURN,ICE,DNS)
http://www.creytiv.com/MjSip
MjSip is a complete java-based implementation of a SIP stack. It provides in the same time the API and implementation bound together into the MjSip packages.
http://www.mjsip.org/NIST SIP
A series of SIP applications, tools and libraries in JAVA.
http://snad.ncsl.nist.gov/proj/iptel/Open Sip Stack
MPL licensed SIP stack with ENUM, Presence (XMPP/SIMPLE) and NAT traversal. Reference implementation of Session Border Controller (OpenSBC) available.
http://www.opensipstack.org/PJSIP
PJSIP is an Open Source Embedded SIP protocol stack written in C. The development of PJSIP is mainly focused on having small footprint, modular, and very portable SIP stack for embedded development purpose (although it's perfectly good for Win32/Linux/MacOS as well).
http://www.pjsip.org/Twisted
Python protocol stacks and applications includes SIP support.
http://www.twistedmatrix.com/SIP SIMPLE client SDK
High level middleware on top of SIP, RTP, MSRP and XCAP protocols
http://sipsimpleclient.org/ivrworx
high level Lua interface to SIP/RTSP/MRCP, for testing distributed VoIP scenarios (windows, Vista+ clients).
http://code.google.com/p/altalena/