Spinner

The Spinner is a gear-shaped spinning-top item found in Twilight Princess.

Location
The Spinner is guarded by the ghostly entity known as Death Sword, in Arbiter's Grounds, the fourth dungeon, though it's unknown since when it has been there. The item also serves as an important weapon against the dungeon's boss, Stallord.

Uses
It is an ancient item created long ago. Link rides the Spinner much like a skateboard, except he can only ride on it for a few seconds until the Spinner loses its momentum. The device can also be attached to railings located on specific walls and allow Link to travel along the railing. It is essential for fully navigating the Arbiter's Grounds as it allows Link to drift across sand without sinking. The Spinner also features a spin attack that Link can initiate to hurt nearby enemies.

The Spinner is useful to break the defenses of the boss, Stallord, first in its main body, and later on his head. It is also the principal item used to unlock the Mirror of Twilight from within the Mirror Chamber after exiting to the roof of the dungeon. After Link leaves the Arbiter's Grounds, the Spinner is rarely required, with the exception of the City in the Sky. Here Link finds some more mechanisms which must be operated using the Spinner, and it can also be used to safely move over the blue tiles which otherwise fall away soon after being stepped upon. The Spinner is also useful to find at least two Heart Pieces hidden in Hyrule Field.

Super Smash Bros. Brawl
The Spinner appears as a sticker in Super Smash Bros. Brawl.

Theory
Because the Spinner is solely used in the City in the Sky to manipulate and power the bridge mechanisms that connect the various floating buildings, it is theorized that the Spinner is perhaps an Oocca creation. Such a claim would rightly connect the Arbiter's Grounds and the City in the Sky, as they both exploit the full capacity of the Spinner as a figment of dungeon navigation. In the Arbiter's Grounds, the Spinner helps that the ancient Sages (who, like the Oocca, are linked to the Goddesses) rest here to guard the Mirror of Twilight; that would maybe link the Oocca to the creation of the Mirror of Twilight. There are also rails connected to the eastern part of Hyrule Field (Wii version) which seems to be right under the City in the Sky.

Trivia

 * If Link uses the Spinner before falling or jumping off a high cliff he'll be slowed down considerably and take no damage upon landing. He can also control his descent as he falls.
 * The final boss from Majora's Mask, during the last part of the battle, throws Link explosive tops that move and spin like the Spinner in Twilight Princess does. The round gear-like platforms found in the staircase of the Tower of Spirits in Spirit Tracks (which take Link back to the lobby of the tower) are similar to the Spinner as well.
 * The Spinner is the only dungeon item in Twilight Princess that doesn't have a targeting cursor.
 * The Spinner can serve a very similar purpose to the Hover Boots.