NVIDIA Freestyle

NVIDIA Freestyle is a technology that allows you to add graphics filters on top of your games in a real time. With Freestyle you can:

Add retro-filter to shooter
Make a picture look like a photo by changing its color and contrast (in ARK Survival Evolved for example)
Change the atmosphere (in Shadow of the Tomb Raider for example)
Set contrast to the max (especially helpful for colorblind people)
Enable night mode and reduce blue color in a game, that will help you to fall asleep after a gaming session.

How lo launch Freestyle?

Open in-game overlay pressing Ctrl+G (Windows) or Cmd+G (Mac)
Press Filter to open Freestyle menu (important: only works in supported games)
In the pop up menu create new style by choosing the preview window and clicking the "+" icon
Add one more filter, clicking the same "+" again
Name a style (preset), make a hotkey for enabling it in the "shortcut" menu.
Hotkeys can be changed in the menu "Settings" > "Hotkeys".
Enable and enjoy while gaming
You can create up to 3 saved styles ( presets). You can add up 15 filters that have 38 different setups. There are hundreds of different combinations in total!