Kamailio

SIP Foundry · Elastix · FreeSWITCH · OpenPBX by Voicetronix · PBXInAFlash · FreePBX · OpenSIPs · ...

OpenSIPS is an Open Source SIP proxy/server for voice, video, IM, presence and any other SIP exte...

Free and open-source license

Asterisk: Open Source PBX with built-in IVR server · Bayonne: GNU project IVR server · CT Server ...