FreeSWITCH is free and open-source server software for real-time communication applications, including WebRTC, video, and voice over Internet Protocol (VoIP). It runs on Linux, Windows, macOS, and FreeBSD. FreeSWITCH is used to build private branch exchange (PBX) telecommunication systems, IVR services, videoconferencing with chat and screen sharing, wholesale least-cost routing, Session Border Controller (SBC) and embedded communication appliances. It has support for encryption, ZRTP, DTLS, and Session Initiation Protocol (SIP). It is implemented as a core library, libfreeswitch, which can be embedded into other projects. It is distributed under the Mozilla Public License (MPL), a free software license.