Multitasking

 
Prerequisite(s): Improved Multiweapon Fighting, Multiweapon Fighting, Multiattack, Int 15+, Dex 15+, 4 or more arms.
 
Benefit: If you have four or more arms, you can use each pair of arms to perform a distinct partial action. All such partial actions occur simultaneously. Thus, you could attack with one or two arms while using a magic item, reloading a crossbow, or casting a spell with two other arms.
 
Source: Savage Species