Program: Riot.im
License: Open Source
Description: Riot (formerly Vector) is an opensource interoperable app running on windows,Web, iOS and Android. It is built around chat rooms, both public and private and provides messaging, filesharing, voice and video conferencing (beta on Android and web), integrations to tools like GitHub, Jira, Jenkins and much more soon. Vector is built on the Matrix.org open standard which provides bridges to other systems such as Slack, IRC and a lot more soon. One can use the hosted service or run their own.
Website: https://about.riot.im/