You can make multiple attacks with your off-hand weapon
Prerequisites: Dex 17, BA +6, Two-Weapon Fighting
Benefit: When you fight with more than one weapon or a double-weapon, you get an extra iterative attack with your off-hand (or one of your off hands) as part of a full-attack sequence. You can take this feat multiple times. Each time, it adds another iterative attack as part of that full-attack sequence. You cannot have more iterative attacks with your off-hand than you already have with your primary hand. You can take this feat multitple times. Each time, it grants an extra iterative attack to your off hand (or one of your off hands).
Example: You have a BA of +12, your off-hand weapon is “light,” and you take both Two-Weapon Fighting and Improved Two-Weapon Fighting. Your full-attack sequence with your primary hand is +10/+5/+0 (because it takes a -2 for two-weapon fighting), and your full-attack sequence with your off-hand is +10/+5. You can now make a single, two-weapon full-attack at +10/+10/+5/+5/+0. Because you took Improved Two-Weapon Fighting only once, it grants only one extra iterative attack as part of the off-hand full-attack sequence. You could take the feat again to gain one last iterative attack on your off-hand, which would give you a full-attack sequence of +10/+10/+5/+5/+0/+0.