
Mumble is a voice over IP (VOIP) application primarily designed for use by gamers, similar to programs such as TeamSpeak and Ventrilo.
Mumble uses a client-server architecture which allows users to talk to each other via the same server. It has a very simple administrative interface and features high sound quality and low latency. All communication is encrypted to ensure user privacy.
Mumble is free and open-source software, is cross-platform, and is released under the terms of the new BSD license. (from Wikipedia, 2013-04-18)