Mumble is a voice chat application for groups. While it can be used for any kind of activity, it is primarily intended for gaming. It can be compared to programs like Ventrilo or TeamSpeak. People tend to simplify things, so when they talk about Mumble they either talk about "Mumble" the client application or about "Mumble & Murmur" the whole voice chat application suite.
but WHAT CAN WE USE THIS FOR?????
full of non-heterosexual persons
we've been having a nice chat with thunder for the last couple of hours