So in Mutants & Masterminds instead of rolling X dice of damage, each attack has a "damage bonus" that the target of the attack makes a saving throw against. The result of the saving throw determines what kind of damage they take: a successful save means no damage, while a failed save means they're hurt. How much depends on how badly they failed the saving throw. A really low save (or a really high damage bonus) can result in an instant knockout.
An added benefit is that you only need a single d20 to play Mutants & Masterminds because everything, from attack and damage rolls to skill and power checks, uses the same basic system.