Wikipedia
Speedboard
The Speedboard is a peripheral accessory for the Nintendo Entertainment System released by Pressman in 1991. The peripheral was a piece of plastic designed to hold the NES controller and allow the player to press the buttons faster without holding the controller in their hands. The Speedboard was the only NES accessory to be endorsed by a NASCAR driver, Kyle Petty.
From an advertisement in Nintendo Power c. 1991:
"The Speedboard, the fastest way to play your Nintendo Entertainment System! Puts the speed at your fingertips! Increase your game scores! Better reaction time and speed! Holds your controller so you don't have to!"