PhysicsJS
The gaming industry trend has evolved from making just simple, plain-old games to considering how real it can get. In FPS games, when you throw a grenade for example, sometimes it bounces off the ground. Sometimes it just rolls away, which is weird.
Introducing Physics to your game makes it more realistic and fun to play. From objects behaving correctly when force is applied on it, to objects falling down with respect to their weight and gravity, I’m sure today’s gamers will appreciate how this kind of feature is applied to a game.
With Physics, even those slow-mo moves Neo did on the Matrix is possible. See samples of different Physics applications here.