Ventrilo is a scalable Voice over IP (VoIP) communications system that solves a lot of the problems associated with network latency, packet loss, uptime and administration.

Ventrilo can be used for home / personal applications like talking to friends and family, or playing organized online games where Voice Comm can make them more exciting and productive. It can also be used in an enterprise environment as a productivity tool for conducting long distance group discussions.
Ventrilo - Scalable Voice Communication Software