Although they haven't made many, Clicker Defense has made attachments for weapons.
The RedScreen is an optical attachment manufactured by Clicker Defense. It is a 1.5x scope. It is rather bulky. It has 4 options, Off, 1 - Lowest Intensity, 2 - Moderate Intensity, 3 - Highest Intensity. It was designed to be a competing option to the AimPoint Comp M4.