Linphone

Linphone is a free, open-source SIP softphone for voice, video, instant messaging and conferencing, developed in France since 2001. It is maintained by Belledonne Communications, founded in 2010 by original creator Simon Morlat and based near Grenoble. Clients run on Linux, Windows, macOS, iOS and Android from a single SIP-standard codebase, and the project is also offered to MSPs, ITSPs and VoIP operators as a white-label professional softphone with commercial support. The core software remains 100% open source under the GNU GPL.