The material below is Open Game Content from the System Reference Document.
IMPROVED MULTIWEAPON FIGHTING [GENERAL]
Prerequisites: Dex 15, three or more arms, Multiweapon Fighting, base attack bonus +9.
Benefit: In addition to the single extra attack a creature gets with each extra weapon from Multiweapon Fighting, it gets a second attack with each extra weapon, albeit at a –5 penalty.
Normal: With only Multiweapon Fighting, a creater can only get a single attack with each extra weapon.
Special: This feat replaces the Improved Two-Weapon Fighting feat for creatures with more than two arms.