Deku Nut

The Deku Nut was a weapon used to briefly stun enemies in The Legend of Zelda: Ocarina of Time and The Legend of Zelda: Majora's Mask.

The Legend of Zelda: Ocarina of Time
Deku Nuts were one of the first weapons Link acquired. Unlike many of the weapons in the game, the Deku Nut could be used by both child and adult Link. The best way to harvest Deku Nuts was to destroy Deku Babas. Sheik also used Deku Nuts to seemingly vanish (as the flash the nuts create caused Link to look away from her). Impa could also do this.

The Legend of Zelda: Majora's Mask
While flying using a flower in Deku form, Link could drop Deku Nuts in flight.

The Legend of Zelda: The Wind Waker
Although you could not have them in your inventory they played a major role in the Forbidden Forest and in the Wind Temple. They could be kicked onto swithes to keep them activated. Due to their hollow interior they can easily be blown around by Deku Leafs.

The Legend of Zelda: Twilight Princess
Their motive in Twilight Princess is similiar to that of their's in The Wind Waker but in Twilight Princess they carry seeds that Link can use in his slingshot.

Super Smash Bros. Brawl
They appeared in brawl as an item that could be thrown at opponents. A direct hit has massive knockback, and anyone in the blast radius will be stunned for a short period of time.