Finesse

Finesse is a Fallout, Fallout 2, Fallout Tactics, Van Buren and Lionheart Trait, as well as a Fallout 3 and a Fallout: New Vegas perk.

Fallout and Fallout 2
All of your attacks do -30% damage. Your critical chance is increased by 10%. The 10% is additive, not multiplicative, meaning a character with 10% critical chance will have 20% critical chance if this perk is taken. Technically, this is done by adding a +30 DR modifier to all attacks, which is ignored by armor-bypassing criticals. And because criticals have a chance to kill an enemy instantly anyway, this is a very good trait.

Fallout Tactics
All of your attacks do -25% damage. Your critical chance is increased by 10%.

J.E. Sawyer's Fallout RPG

 * -2 to damage, +2 to attack rolls for purposes of determining critical hit results.

Fallout 3 and Fallout: New Vegas
This perk grants an extra 5% chance to land a critical hit upon an opponent regardless of the player's Luck attribute. This bonus is affected by a Weapons critical multiplier.

Strategy
Although an extra 5% critical chance is undoubtedly helpful to any character, combining Finesse with other critical-enhancing effects ensures you get the most bang for your buck.
 * Taking the Better Criticals Perk increases critical damage by 50%.
 * Using a weapon with a critical multiplier, such as the hunting rifle or bladed gauntlet, greatly increases your chances of a critical without using an extra perk. A character with a 5 Luck, Finesse, and a hunting rifle has a 20% critical chance outside of V.A.T.S.
 * In Fallout: New Vegas, the Built to Destroy Trait increases critical chance by 3% while increasing the rate at which your weapons degrade.

Characters with very low Luck arguably do not benefit as much from Finesse, as they are not typically reliant on critical chance to be effective. This also holds true for characters that almost always attack from stealth - sneak attacks are always criticals and do not rely on critical chance.