Weeping Blades, Fighting Claws, Asrai Blade-staff just to mention some. All have the special rule "Additional Attack" or "Pair", which practically does the same rulewise. In the case of Weeping Blades and Fighting Claws, it's about a weapon combination consisting of two weapons, where in the Blade-staff case, it's a single weapon with this rule, much similar to wielding a Halberd or a Double-handed Weapon.
As we play it atm., there's no dual-wielding penalty with Weeping Blades and Fighting Claws, nor is there a penalty when using the Blade-staff, because it's a special rule as indicated by the RAW. However, does everyone else play it like that? And is there some sort of balance issue with this solution?
I'd love to hear some comments on this!