Monitor Brightness Management App
"Twinkle Tray lets you easily manage the brightness levels of multiple monitors. Even though Windows 10 is capable of adjusting the backlight on most monitors, it typically doesn't support external monitors. Windows 10 also lacks any ability to manage the brightness of multiple monitors. This app inserts a new icon into your system tray, where you can click to have instant access to the brightness levels of all compatible monitors.
It's built with Electron, React and Node.js."