The Pinnacle Pro-ONE Overlay Windows Driver is a driver for a professional video capture and editing card, the Pinnacle Pro-ONE. The Pro-ONE card is used for high-quality video capture, editing, and output, typically in professional video production environments. The overlay driver specifically allows the card to output a live video preview on a monitor or external device, which is often used during editing to see real-time effects and transitions, or for monitoring playback on a professional display.

In essence, the overlay driver lets you use the Pro-ONE card to create a "video overlay" on your monitor or external screen, providing a live preview of your video project during editing. This is crucial for video production workflows that require real-time monitoring of video effects, transitions, and cuts.