Mumble is a free and open source audio chat software that has a goal to offer everyone ability to chat in a group environment. This includes setting up an audio call with large amount of people for school project, business meeting or (most often) organized video gaming.
This and many other online communication sessions can be greatly enriched with the help of Mumble, which can take control over management of user permissions and other features that will be attractive to moderators who want to tightly control who can talk with who (especially important for use in business, or in gaming with separate rooms for each gaming sessions, group or game).
Mumble is there to help you do just that with ease. Users can host their own servers, invite users to manage their own channels, record their audio sessions and manually control when they want to mute their own microphone or mute incoming audio communication.