MonitorControl - Control your external monitor brightness&volume on your Mac

Dimmer - A very small and free utility for Windows to reduce brightness on LCD/TFT screens.

Lunar.fyi - Control monitor brightness, adapt using the ambient light sensor, adjust volume, switch inputs and turn off displays without fiddling with clunky buttons.

CareUEyes - CareUEyes is an eye protection software for windows that comes with blue light filter, screen dimmer, and break reminder

Screens - GNU Screen.

LightBulb - Background application that adjusts screen gamma, making the colors appear warmer at night...