Tinytalk is a small free application which will allow you to call another one if you know the IP of his computer. It can also be used as an intercome in your office :)

Details from the website

Features and Details:
• Very tiny single exe streams 8 bit PCM voice data at 11.025KB/s in Full Duplex operation.

• Automatic Silence Detection; audio transmission will pause after 3 seconds of silence occurs.

• Hold to Talk, and Toggle to talk keys allow easy control over possible feedback conditions.

• Single TCP port operation, the port is user configurable.

• Docks to system tray for easy background running operation.

• Automatically stores IP's of connected and Received connections.

• Send and Receive audio level meters for visual monitoring.

• -m switch will minimize the application to the system tray on startup.

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