The triple dagger (Arms and Equipment Guide 6, 10) (10 gp; 1 lb.) is—with some minor adjustments due to the Dungeons and Dragons 3.5 revision—a light exotic melee weapon that deals 1d4 points of damage and has a critical of 19–20/×2. In addition, it has this untouched description:
This weapon is used in the off hand as a means to disarm an opponent—you hold it as you would a shield, not another weapon, and so do not take penalties for fighting with two weapons. When using a triple dagger, you get a +3 circumstance bonus on your opposed attack roll when attempting to disarm an opponent (including the roll to keep from being disarmed if you fail to disarm your opponent). The triple dagger could also be used as a normal dagger, if desired, but if used in the off hand, all normal penalties for fighting with two weapons apply.
Emphasis mine. Is that boldfaced text misunderstanding how two-weapon fighting works? (That is, a creature is two-weapon fighting when it attacks with two separate weapons not when it merely wields them.) Or is that boldfaced text saying that, when the triple dagger occupies the same position a shield would, the creature can two-weapon fight using the triple dagger as its off-hand weapon and make all its two-weapon fighting attacks without suffering any two-weapon fighting penalties? Or is there another way of reading this weapon's description?
Note: While from a Dungeons and Dragons, Third Edition source, the triple dagger is, so far as I'm aware, never updated to Dungeons and Dragons 3.5. Hence the version presented here is post- 3.5 revision game-legal. Tags reflect both this weapon's provenance and the potential of the asker to use the weapon in a 3.5 campaign. While I'd prefer a rules-as-written answer, because the 3.5 revision explicitly permits the DM to make minor adjustments to unrevised 3e material, other answers that hew closely to the rules are fine.