third-party add-ons are free; a few even support embedded platforms such as the Raspberry Pi. See also Comparison of VoIP software DUNDi FreeSWITCH IPBX GateKeeper H.323 GNU SIP Witch List of free and open-source software packages List of SIP software OpenBTS SIP Express Router References External links Free VoIP software Free business software Free software programmed in C Free communication software Telephone exchange equipment Videotelephony Lua (programming language)-scriptable software 1999 software