A Rhotuka launcher was a tool, either natural or artificial, capable of hurling an energy spinner long distances at a target. They were used for both offense and defense. Some beings, including some Rahi, had natural launchers as part of their bodies. Others carried mechanical launchers.
The Dark Hunter Guardian had his arm rebuilt to allow him to wield a staff that launched Rhotuka spinners.
There were no artificial Rhotuka launchers on Metru Nui before the Visorak invasion because the island hadn't received any in trades.