Channel Listeners (new Mumble/Murmur feature)
Interesting new feature in the Mumble master branch (future 1.4.x).
https://github.com/mumble-voip/mumble/pull/4011
This implements #3319 by allowing users to "listen" to a channel they have not joined. Doing so will place a "listener proxy" (in other software this is sometimes known as a "phantom") in that channel which will look like a normal user except that it'll have the same name as the user listening to that channel and an ear-icon instead of the normal avatar-icon. It will also always show a muted-icon next to it.
If a listener proxy is in a channel, the server will route all audio packets from that channel to the user the proxy belongs to (as if that user was in the channel). Note though that the opposite of this is not true: The users in the channel will not hear audio from the listening user unless that user decides to join the channel.