From Wiki of Worlds Unknown
Improved Two-Weapon Fighting (Combat)
- Dex 17, Two-Weapon Fighting, base attack bonus +6.
- You gain the same number of iterative attacks with your off-hand weapon that have for your primary weapon.
- Without this feat, you can only get a single extra attack with an off-hand weapon.
Greater Two-Weapon Fighting (Combat)
- Dex 19, Improved Two-Weapon Fighting, Two-Weapon Fighting.
- Anytime you are entitled to make a single melee attack as part of a standard or full-round attack action, you may also make an attack with your off-hand weapon.