Swarmfighting( Races of Faerûn, p. 169)
You and allies with this feat can coordinate melee attacks against a single target and are adept at fighting side by side in close quarters.
DEX 13, base attack bonus +1, Size Small,
You can occupy the same 5-foot square in combat with any other allied Small or smaller creature that also possesses the Swarmfighting feat. Up to four creatures of Small size may occupy a 5-foot square (creatures one size category smaller count as half a creature). When you attack a Medium-size or larger creature with a melee attack, and at least one other ally with the Swarmfighting feat threatens the target, you gain a +1 morale bonus on the attack roll. This bonus increases by +1 for each additional ally beyond the first with the Swarmfighting feat who threatens the same target. The total morale bonus imparted to your attack roll cannot exceed your Dexterity bonus.