Kote

The is a  developed by Katasuke of Konohagakure's Science Ninja Weapons Team.

Overview
As its name suggest, this tool is worn on the forearm. The user seals one of their techniques into a small scroll and puts it inside the Kote. Afterwards, they can release the scroll and use the sealed technique. To use an elemental technique, the user apparently needs to form the corresponding seal first. Because using the Kote doesn't require chakra, the user can gain an advantage in battle by releasing normally chakra-taxing techniques while saving his chakra or continuing to use techniques when low on chakra.

Trivia

 * Masashi Kishimoto thought of a tool like this since before Naruto began. However, he could never introduce it into the manga.