Ventrilo
Ventrilo is a scalable Voice over IP communication program created by Flaship Industries, Inc. Users download the Ventrilo client and then connect to a Ventrilo server. Users usually communicate through use of a headset or a microphone, but these are not required to run Ventrilo. Default sound quality is similar to a telephone's sound quality, but the quality can be changed by switching to a different codec.
Ventrilo is often used for online gaming when reflexes are an issue and time cannot be wasted typing out responses. Rather, gamers use Ventrilo to communicate with members on the same team as them for tactical reasons. Some outfits in PlanetSide use Ventrilo, and some go as far as to mandate Ventrilo to be a member of the outfit.