MonitorControl - Control your external monitor brightness&volume on your Mac
Lunar.fyi - Control monitor brightness, adapt using the ambient light sensor, adjust volume, switch inputs and turn off displays without fiddling with clunky buttons.
Duet Display - With Duet Display, you can transform your iPhone or iPad into a second display to expand the screen space of your PC or Mac system.
Screens - GNU Screen.
DisplayBuddy - Control the real brightness of your monitors directly from your Mac - no need to touch the buttons on your Monitor.
mRemoteNC - mRemoteNC is the next stage of mRemote development