Realistic Encumbrance is a mod for Witcher 3 that aims to bring a realistic encumbrance for weapons and armors, not unlike what The Witcher 1 offered. The idea is to equip your weapons and armor with a set amount of a specific kind of weapon or armor, and the more you have, the more you will weigh. This is to make it more difficult for you to fight, and it works by adding a new kind of item to your game.

So if you are a huge fan of The Witcher series, you can download it for free, install it in your game, and you can play it as you are a totally free player.