Hyperdrive attenuators were tools used to work on hyperdrives. The Besalisk cook Dexter Jettster traded Furbogs for at least one during his time traveling the Corellian Run.
Behind the scenes
Hyperdrive attenuators are possibly similar to real world attenuators which are used to reduce the amplitude or signal of a device.
Sources
Dining at Dex's on Hyperspace (article) (content obsolete and backup link not available) (First mentioned)