FreeSwitch is a free, open-source application server for real-time communication. It is used to build PBX (private branch exchange) systems, video conferencing and IVR (interactive voice response) services. The server is supported cross-platform, and is used with MacOS, Windows, Linux, Solaris and multiple BSD (Berkeley Software Distribution) descended operating systems of which FreeBSD is the most popular.
FreeSwitch is licensed under a free software license, giving a recipient the ability to adapt and redistribute the software. There are still restrictions, as FreeSwitch is not in the public domain.Ajiri FreeSwitch Developers