Mumble was the primary choice for EVE Online groups.

You can literally have thousands of users on the same server.

In EVE, during big fleet fights (like 1000+ people on the same “team”), you can have a hierarchy of fleet commanders/wing commanders/squad leaders where voice travels down the chain of command, but not up.

Also the certificate based security with ACLs is just unmatched. You can set it up exactly how you want.

Also easy to integrate with, which is important for something like EVE.