TeamSpeak

TeamSpeak is flexible, powerful, scalable software which enables people to speak with one another over the Internet. TeamSpeak consists of both client and server software. The server acts as a host to multiple client connections, capable of handling literally thousands of simultaneous users. This results in an Internet-based conferencing solution that works in a variety of applications such as teammates speaking with one another while playing their favorite online game, facilitating inter-office communication among co-workers, or simply for personal communication with friends and family.

Client software

Address book for easier management of multiple TeamSpeak servers
Server browser that allows you to search for public TeamSpeak servers on the Internet
Create multiple channels and sub-channels for your users
Configure individual channels with different codec settings
Moderate channels for more control when hosting large group meetings
Toggle group or channel leaders as "Channel Commanders" to improve ommunication
Assign key-bindings for instant private chat and other functions
Whisper functions so you can speak privately to inidividuals, groups of persons, or users in other channels
Kicking/banning features which allow you to get rid of problem users in seconds
Embedded automatic normalization of your microphone's input volume
Record conversations via the client in native WAV format

Server software

Create your own server for private conversations or complete control
Virtual server instancing (ideal for "server farming")
Protect your server or channels with passwords for privacy and security
Command line, telnet based access to your core server and all it's virtual instances
Configure server settings remotely using your favorite web browser
Modify your server name, server password and other settings via the web administration interface
Also modify feature-rich group permission settings for various user types
Support for clickable web URLs in welcome messages and channel descriptions
... and MUCH MORE!