You can rend opponents when fighting with more than two limbs.
Prerequisites: Dex 15, base attack bonus +9, three or more hands, Multiweapon Fighting.
Benefit: If the character hits an opponent with two or more weapons (wielded in different hands) in the same round, he or she may automatically rend the opponent. This rending deals additional damage equal to the base damage of the smallest weapon that hit plus 1½ times the character’s Strength modifier. The character can only rend once per round, regardless of how many successful attacks he or she makes.
Special: This feat replaces the Two-Weapon Rend feat for creatures with more than two arms.
Source: Standard Reference Document under Open Game License v1.0a, which updated this feat originally published in the Epic Level Handbook, page 63. (Point of interest: the SRD referenced Two-Weapon Rend, which doesn’t appear until the Player’s Handbook II, which was published later than the SRD.)