From https://ring.cx/ :
Free download for GNU/Linux, Mac OSX, Windows and Android.
[video=youtube;uOHeSxKCiN4]https://www.youtube.com/watch?v=uOHeSxKCiN4[/video]About Ring
Ring is a free software for communication that allows its users to make audio or video calls, in pairs or groups, and to send messages, safely and freely, in confidence.
Savoir-faire Linux and a community of contributors worldwide develop Ring. It is available on GNU/Linux, Windows, Mac OSX and Android. It can be associated with a conventional phone service or integrated with any connected object.
Under this very easy to use software, there is a combination of technologies and innovations opening all kinds of perspectives to its users and developers.
Ring is a free software whose code is open. Therefore, it is not the software that controls you.
With Ring, you take control of your communication!
Confidentiality:
No personal information is stored on a central server. It is therefore impossible to create files on users. Anonymity and respect for privacy are guaranteed.
Security :
Trade security is ensured by encryption methods and the use of certificates. Audio, video and text are converted into a coded message that only the recipient can decrypt.
Freedom:
Ring is an open source software under the GPL v3 license. Everyone can verify the codes and propose new ones to improve the software's performace. It is a guarantee of transparency and freedom for everyone!
Free download for GNU/Linux, Mac OSX, Windows and Android.