Monitorian - Monitorian is a Windows desktop tool to adjust the brightness of multiple monitors with ease.
CareUEyes - CareUEyes is an eye protection software for windows that comes with blue light filter, screen dimmer, and break reminder
Twinkle Tray - Easily manage the brightness of your monitors in Windows from the system tray.
Dimmer - A very small and free utility for Windows to reduce brightness on LCD/TFT screens.
PangoBright - Screen dimming software that allows you to control the brightness of your laptop screens as well as external monitors.
Red Moon - Screen filter for night time phone use.