Agility

Agility is an Attribute that grants Armor and Attack Speed. For every point of Agility a Hero has, their Attack Speed goes up by 1 and their Armor increases by 0.14, meaning Heroes gain roughly 1 Armor for every 7 points of Agility. For Agility heroes, every point of Agility increases their damage by 1.

Agility Heroes
Because Agility heroes are the only class of heroes to gain both damage and attack speed as their primary attribute increases, they tend to have the highest physical damage output as the game progresses. This makes them scale very well with offensive items. They tend to have limited disabling capabilities or nukes; almost all their abilities augment their physical capabilities or serve as positioning or escape mechanisms. This tends to make them a lot more vulnerable and weak in the early game when strong offensive disables and nukes dictate the flow of kills, but also means that, with good items under their belts, they will be the ones delivering the greatest amount of damage in the late game, while also being dealt the least amount of physical damage as a result of their high armor. Agility heroes have a roughly even split between being melee or being ranged, and fit primarily into carry and ganker roles.

At the moment, there are Agility Heroes implemented in Defense of the Ancients, and  implemented in Dota 2.

Below is a table of all Heroes with Agility as their primary attribute. The growth columns indicate by how much the base values will increase for each level of the hero.