Guild Wars 2

Both disable movement and attacks.

Both are escaped with stun breakers.

Both are negated if you have stability.

Why have 2 forms of CC that perform exactly the same purpose?

Knockdown tends to cause a bit of movement and can’t be broken as quickly as a Stun. Any player who uses stun breakers will tell you that stuns are preferable to knockdowns because triggering a stun breaker on a knockdown too quickly can keep the stun breaker from breaking the knockdown.

It’s also better in a design perspective so that you have the same effect with two ways to express it based on what caused the effect. It wouldn’t make sense for the Elementalist’s Earthquake to cause Stun or Pistol Whip to cause knockdown.

stun is a condition so it’s removable.

Smirgel.9460:

stun is a condition so it’s removable.

Main and most important difference. Knock downs cant be removed as conditions do.

hharry.1967:

Smirgel.9460:

stun is a condition so it’s removable.

Main and most important difference. Knock downs cant be removed as conditions do.

Stun isn’t a condition. It’s a control effect (http://wiki.guildwars2.com/wiki/Control_effect). The only alike condition is immobilise and it doesn’t prevent usage of skills.