Escape Artist lets you kill a smaller enemy right after you break free from its grapple. It is a Tier 1 Melee skill and one of the most useful early buys, because Swarmers grab you constantly.
Yes, early. Being grabbed is the most common way a fight turns on you, and this turns every grab into a kill.
Executioner later in the tree, and Busted Up, since the grapple kill counts as a melee kill.
Watch for the prompt the moment the grapple breaks. Miss it and the enemy simply staggers back into the fight.
Bull Rush
Lets a sprinting melee attack stun a regular human or a Swarmer.
Busted Up
Restores some stamina with each melee kill.
Executioner
Lets you stealth attack heavy Freakers, and kill heavy Freakers or large animals when breaking a grapple.
Field Repairs
Lets you fix melee weapons using scrap.