CORE - Character Oriented Roleplaying Engine is a very concise roleplaying mechanism that uses a single method for determining all contested actions, including combat. The basic rules are solid but not completely developed.
Characters have five "Characteristics" (Strength, Speed, Will, Reason, Creativity) with values assigned from a pool of 20 points. Values must be between 1 and 6.
Characters then select Skills and assign a "Skill Rating" to each skill from another pool of 20 points. Selected Skills must have at least one point allocated and cannot have more points allocated than the value for the Characteristic linked to the Skill. In this system, combat ability is a skill, including: Aiming Skill (firearms), Archery, Axe Weapons, Blade Weapons, Club Weapons, Shield, Thrown Weapons, Thrusting Weapons, and Unarmed Combat. Characters that do not take any combat-related skills cannot participate effectively in combat. A successful combat use of combat Skills may not deal damage if the opponent in turn successfully utilizes a defensive Skill. There is no mechanism noted for advancing Skill Ratings.
Damage usually ranges from 0 to 7 and is applied to the value of a Characteristic, which in turn will decrease Skill performance for Skills linked to the damaged Characteristic. Generally, Damage is first applied to Strength or Speed until those scores are reduced to zero, then Damage is done to Will. When Will is reduced to zero the character dies.
When an action is critical or opposed, the GM will call for a Skill check which is made using 2d6; the roll must be under the Skill Rating for success (the rules do not specify what happens if the roll equals the Skill Rating. Various degrees of success are possible depending on the roll, namely: Success, Superior Success, and Critical Success.
The document lists thirty-nine Skills and states that each Skill has component "Secondary Skills", but these are not given in the rules except for Agriculture (Animal Husbandry, Horticulture) and an inferred Attack and a stated Parry under each hand weapon skill, or Attack and Dodge for Unarmed Combat.
Finally, the Speed Characteristics determines how many separate actions a character can complete in a single round of combat. Each action has a speed cost (not noted in the rules) which is subtracted from a Speed Characteristic pool (renewed each round). When the pool is expended the character can no longer act.
Note that as published, the rules would be difficult to use for a campaign; an experienced GM would have to make numerous assumptions and extensions.