Mac: Trying to look at a bright screen at night sucks, and it's annoying for pretty much everyone around you. Tranquility is an app that puts an option in your menu bar to instantly switch over to a dark, monochrome look to help reduce eyestrain.
Macs have always had the ability to invert colours as an Accessibility feature, but Tranquility adds a lot of options so you can optimise the mode to fit your preferences. You can use a monochromatic view, change the colour palette, hide the menu bar, get rid of shadows and easily adjust the brightness.
Basically, if you're stuck working on a screen at night, Tranquility makes it super easy to quickly switch over to a more readable screen.