OK, these were inspired by some of the 3.5 Feats and Classes, but I'm posting them here since they aren't direct ports of the original sources.
Dual Weapon Proficiency:
Chose one type of dual weapon. You can now use that weapon in the manner it was intended.
Prerequisite: Base attack bonus +1
Benefit: You may make attack rolls with the weapon normally, and may fight with the weapon as if you possessed the Two-Weapon Fighting feat.
Special: You may take other feats which require the Two-Weapon Fighting feat, however, they may only be used when using the weapon selected with this feat unless you meet the requirements otherwise.
Dual Weapon Focus:
Prerequisite: Dex 15, Two-Weapon Fighting, Weapon Focus with a dual weapon, base attack bonus +4
Benefit: When fighting with a dual weapon, you can a +1 bonus to your attack rolls and AC. If you have the Improved Two-Weapon Fighting feat, this bonus becomes +2, and if you have the Greater Two Weapon Fighting feat, this bonus improves to +3.
Tempest Defense:
Prerequisites: Dex 17, Two-Weapon Defense, Two-Weapon Fighting, base attack bonus +6
Benefit: When wielding a double weapon or to weapons (not including natural weapons or unarmed strikes) your shield bonus from Two-Weapon Defense increases by +1. If you have Improved Two-Weapon Fighting, it increases by +2, and if you have Greater Two-Weapon Fighting, it improves by +3.
Your bonus when fighting defensively or using the total defense action is increased by the same amount.
Two Weapon Spring Attack:
Prerequisites: Dodge, Improved Two-Weapon Fighting, Mobility, Spring Attack, Two-Weapon Fighting, base attack bonus +8
Benefit: When making a spring attack, you may attack one each with two different weapons. You take all the normal penalties for attacking with two weapons during this attack.
Normal: You may only attack with one weapon during a spring attack.
I did the dual weapon proficiency because I think most of the exotic dual weapons are a serious screw job for a player. EWP states you learn to use the weapon, along with all its special manuevers, but it still takes TWF to use an exotic dual weapon to complete effect. Seemed a little harsh.
The others were insprired by the exotic weapon master and tempest classes.
Let me know what you think.