Ring is free software which allows its users to communicate in multiple ways.

What is Ring?

  A telephone: a simple tool to connect, communicate and share.

  A teleconferencing tool: easily join calls to create conferences with
  multiple participants.

  A media sharing tool: Ring supports a variety of video input options,
  including mutliple cameras and image and video files, and the selection of
  audio inputs and outputs; all this is supported by multiple high quality
  audio and video codecs.

  A messenger: send text messeges during calls or out of calls (as long as
  your peer is connected).

  A building block for your IoT project: re-use the universal communications
  technology of Ring with its portable library on your system of choice.