Ventrilo is the next evolutionary step of Voice over IP (VoIP) group communications software. Ventrilo is also the industry standard by which all others measure themselves as they attempt to imitate its features.
Ventrilo connects to Servers in the whole world or to one in your Local Network. Just login and enter a available room. The freeware version permitts 8 clients per room. You can use several audiocodecs, the sound output can be configured with surround sound. There is also a pro version, but this is reserved for professional hosting-services.