Before I forget, each class starts out with a basic skill and a class ability. Class abilities are passives that belong to class types, rather than individual classes (so all offensive magic classes will learn the same class abilities, no matter what they promote to, etc.).
Defensive:
Basic Skill: Forward Charge - The knight charges forward, bashing into his target. This skill has a small chance to stun the enemy, which increase as they level up the skill.
Class Ability: Derision - Basic attacks and skills generate higher amounts of Hostility (higher chance of the enemy switching aggro to the attacker).
Offensive Melee:
Basic Skill: Slice n' Dice - The fighter strikes his target twice, lowering their Defense. The amount of defense lowered increases as they level up the skill.
Class Ability: Pinpoint - Critical attacks deal 20% more damage.
Offensive Ranged:
Basic Skill: Crippling Shot - The hunter fires at the target's feet, slowing their movement speed. The length of the slow increases as they level up the skill.
Class Ability: Camouflage - Basic attacks and skills generate lower amounts of Hostility (lower chance of the enemy switching aggro to the attacker).
Offensive Magic:
Basic Skill: Magic Missile - The mage fires a bolt of magical energy at a target.
Class Ability: Recycle - Spells that hit nothing will refund 20% of their mana costs.
Support:
Basic Skill: Heal - The cleric heals an ally for a small amount of health.
Class Ability: Unwavering Faith - Higher immunity to negative status conditions.