Belledonne Communications | Linphone

Linphone is an open-source real-time communication project developed for over 20 years by Belledonne Communications. It provides a complete, modular, and interoperable solution for audio/video calls, instant messaging, and video conferencing. Based on the SIP protocol, its ecosystem includes three main components: the Linphone softphone, the Liblinphone SDK, and the Flexisip server suite. Linphone is an open-source alternative to proprietary solutions, including GAFAM platforms.

Website: https://www.linphone.org/en/
Source code: https://gitlab.linphone.org/BC/public
Community space: https://www.linphone.org/en/community/
Free SIP service: https://subscribe.linphone.org/register/email