Multiweapon Fighting( Monster Manual II, p. 18)
A creature with three or more hands can fight with a weapon in each hand. It can make one extra attack per round with each weapon.
Three or more hands,
Penalties for fighting with multiple weapons are reduced by 2.
This feat replaces the Two-Weapon Fighting feat for creatures with more than two arms.
A creature without this feat takes a -6 penalty on attacks made with it's primary hand and a -10 on attacks made with it's off hands. (It has one primary hand, and all others are off hands.) See Attacking with Two Weapons, page 124 in the Player's Handbook.